Air heater for mobile applications with reduced housing surface temperature

Abstract

A fuel-based air heater for a vehicle comprises an assembly (35, 36) for generating heat, a heat exchanger (30) thermally cooperating with the assembly (35, 36), an outer housing (G) that accommodates the assembly (35, 36) and the heat exchanger (30), wherein the outer housing (G) and the heat exchanger (30) form at least one heating air duct (39) between them, the latter being formed by an inner wall (70) of the housing (G) and an outer wall (29) of the heat exchanger, and a heating air blower (14) that is configured to draw in heating air via an intake opening (11) of the outer housing (G) and convey it along a flow direction (49) through the at least one heating air duct (39) and discharge it via an outlet opening (12).Furthermore, a separating element (50) is provided, which is arranged in the at least one heating air duct (39) and extends in a section (40) of the heating air duct (39) along the flow direction (49) determined by the operation of the heating air blower (14). In this section (40), the separating element (50) divides the heating air duct into an inner heating air duct section (52), which is defined between the separating element (50) and the outer wall (29) of the heat exchanger (30), and into an outer heating air duct section (54), which is defined between the separating element (50) and the inner wall (70) of the housing (G).

Description

Technical field:

[0001] The present invention relates to an air heater for mobile applications with a reduced housing surface temperature. Technical background:

[0002] Air heaters for mobile applications, particularly in vehicles or construction machinery, are conventionally fuel-based. In a combustion chamber, heat is released by means of fuel supplied from a tank. The hot combustion gases transfer some of their usable heat energy to heated air, which is supplied by a fan, in a heat exchanger. The air to be heated (also referred to as heated air in this document) is generally drawn over the heat exchanger by a fan, typically a single-walled outer casing. Such casings serve primarily to direct the airflow.

[0003] An outer casing can comprise one or more housing shells, usually made of plastic. The outer casing, or the corresponding housing shell, is mounted on the air heater in such a way that there is a slight gap to the outer fins, which extend outwards from the base of the heat exchanger. This gap creates one or more channels for the heated air, through which the fan can circulate the heated air. The outer casing, or the corresponding housing shells, essentially define the outer contour of the entire air heater.

[0004] The fins of the heat exchanger increase the contact area between the heat exchanger and the heated air in the relevant hot air duct and guide the heated air in individual flow channels between the fins. This ensures efficient heat transfer between the heat exchanger and the heated air. The heated air warms up along the resulting flow path and is then transferred to a downstream application, such as a hose system with one or more outlet openings in the vehicle's passenger compartment.

[0005] In the case of single-walled outer casings or corresponding casing shells, an undesirable effect can occur: the guidance of the heated air along the inner surface of the casing shell(s) leads to increased convective heat transfer to the shell(s). Furthermore, heat can also be transferred via radiation across the gap from an outer surface of the heat exchanger—that is, from both the base body and the fins—to the casing shell(s). Consequently, the single-walled casing shell(s) can reach significantly elevated temperatures on a touchable outer surface of the air heater, potentially exceeding 50 °C.

[0006] As a result, contact could lead to injuries or burns. To prevent this, the European Economic Commission (ECE) has established permissible surface temperatures for vehicle heating systems in regulation ECE R-122, which are binding for manufacturers. Manufacturers must therefore design their air heaters to comply with these regulations.

[0007] For newer air heating systems, however, the demand for higher power densities, or in other words, for greater compactness, is increasing. This is accompanied by a simultaneous demand for a wider heating output range, particularly a higher maximum heating output. This requirement can only be met by using a highly efficient and compact heat exchanger. Consequently, as described, the housing shells and outer casing are also very compact.

[0008] As a result, with the same arrangement as in the prior art, more heat must be transferred to the shells per unit area, which is almost impossible to prevent. This inevitably leads to an increase in surface temperatures compared to conventional heating devices.

[0009] This can lead to a high heat transfer coefficient on the inside of the housing, particularly in areas of the respective heating air duct where the heating air is redirected, and consequently to increased heat input into the outer housing or the relevant housing shell. For single-walled housing shells in a state-of-the-art arrangement, this can result in permissible surface temperatures of 80 °C in steady-state heating operation and 110 °C in case of overheating, as specified in Regulation ECE R-122 (Annex 5, point 2), potentially being exceeded under certain operating conditions. Description of the invention:

[0010] The present invention is therefore based on the objective of providing an air heater in which, even with a compact design and higher volumetric power density, the temperatures occurring on an outer surface of an outer casing, in particular locally occurring maximum temperatures, are kept within a range that does not endanger persons and / or the limit values ​​specified, for example, in accordance with regulation ECE R-122 (or in accordance with the analogous regulations applicable in third countries or regions) for the surface temperature are complied with.

[0011] According to various aspects of the invention, an air heater for mobile applications, e.g., for a vehicle, is proposed, which may in particular be a fuel-based air heater. However, according to these aspects, it is also not excluded that the heat generation is powered by an electrical energy source. The term "vehicles" includes passenger cars, commercial vehicles, motorhomes, trailers for passenger cars or commercial vehicles, caravans, construction machinery, or motor- or sail-powered ships or houseboats, etc., and the aspects are not limited to specific applications.

[0012] The air heater comprises a heat-generating assembly and a heat exchanger that thermally interacts with the assembly. The heat exchanger is designed to absorb the heat energy generated by the assembly and transfer it to a medium, in particular heated air. For this purpose, the air heater also has an outer casing that houses the assembly and the heat exchanger. The outer casing and the heat exchanger form at least one heated air duct between them, defined by an inner wall of the outer casing and an outer wall of the heat exchanger. In this heated air duct, the heated air can be guided over or past the heat exchanger to absorb heat from it. To form the heated air duct, the outer casing can be spaced apart from the heat exchanger. The outer casing thus defines the outer boundary of the heated air duct.

[0013] The outer casing can have a single- or multi-layered construction. This means that two or more casing layers can be present, which—complementing each other—form an interior space in which (among other things) the heat generation assembly and the heat exchanger are housed. In the case of a multi-layered construction, it is possible, and indeed preferred, that only one of the casing layers, with its inner wall (which is only a part of the inner wall of the outer casing), faces the outer wall or surface of the heat exchanger, thereby forming the hot air duct.

[0014] Preferably, the outer casing, or at least the casing shell opposite the heat exchanger, is single-walled. This does not preclude a multi-layered structure for this single wall. The presence of individual design-related cavities within the outer wall is acceptable.

[0015] The air heater further comprises a hot air blower configured to draw in hot air through an intake opening in the outer casing and convey it along a flow direction through at least one hot air duct, discharging the hot air through an outlet opening in the outer casing. In a preferred embodiment, the hot air blower is positioned upstream of the hot air duct (against the flow direction). This can thermally relieve the drive or motor of the hot air blower, as well as any corresponding impeller and its bearings.

[0016] A defining characteristic of the aspects presented here is a separating element arranged in the at least one hot air duct that forms between the outer surface of the heat exchanger and the housing. The separating element extends along a section of the hot air duct in the direction of flow determined by the operation of the hot air blower. This section could conceivably also extend the entire length of the hot air duct in the direction of flow. However, a partial section of the hot air duct is preferred. In the latter case, this means that—viewed longitudinally—the separating element is arranged in the aforementioned section of the hot air duct, but not in a further section. Viewed circumferentially, however, the separating element preferably completely encloses the heat exchanger.

[0017] It should be noted that the hot air duct is defined here by a gap or space between the outer casing (or casing shell) and the heat exchanger. Within the air heater, this hot air duct may be preceded by a duct that bridges the gap between the hot air blower, which may be located, for example, near the intake opening at one end of the air heater, and the heat exchanger. This duct and the hot air duct may merge directly into one another.

[0018] In this section, the partition divides the heated air duct into an inner section, located between the partition and the outer wall of the heat exchanger, and an outer section, located between the partition and the inner wall of the housing. This division splits the heated air flowing through the duct at the inlet into two parallel flows. However, these two sections still conceptually constitute the entire heated air duct.

[0019] The separating element is preferably designed as a thin wall (to avoid obstructing the heated air duct, which would lead to increased air resistance and thus require higher fan power) that extends between the two heated air duct sections and separates them. In the inner heated air duct section, the heated air remains in contact with the outer wall or surface of the heat exchanger and continues to heat up as it travels. The partial flow conveyed in the outer heated air duct section, on the other hand, heats up only to a limited extent, namely no longer through direct convective heat transfer via contact with the heat exchanger, but essentially only via contact with the separating element. As a result, a comparatively smaller amount of heat is transferred to the inner wall of the outer casing (or surface) in the section where the separating element is located.the corresponding housing shell) is transferred, with the result that the temperature reached on the outer surface of the outer housing is also reduced compared to a (conventional) case in which no separating element is provided.

[0020] However, aspects and embodiments of the invention provide that the heated air ultimately delivered for subsequent applications (e.g., passenger compartment heating, etc.) comprises both components: not only the heated air that is further heated to a high temperature in the inner section of the heating air duct, but also the heated air that is moderately heated in the outer section. Some embodiments described below therefore provide for the two partial flows to be recombined within the air heater before being discharged through the discharge opening, so that the absorbed heat from the outer partial flow is also utilized and the overall heating output is made efficient.

[0021] Preferably, both the inner and outer sections of the heated air duct are connected, on their side defining the inlet area for heated air, against the direction of flow of the heated air, to an undivided section of the heated air duct that extends continuously and without barriers (without a separating element) from the inner wall of the outer casing to the outer wall of the heat exchanger. Within this undivided section of the heated air duct, the conveyed heated air can therefore warm up during operation to a point where the heat transfer from the heated air to the outer casing exceeds a critical limit. Without further measures, this would lead to a surface temperature being reached at a point downstream on the outer casing that would no longer be compatible with, for example, the aforementioned regulation ECE R-122 (Annex 5, point 2).However, by separating the flow of heated air into partial flows using the separating element, the further increase in surface temperature is now kept within limits.

[0022] The inlet area can be formed by an inlet edge of the partition element. In the case of an upstream, undivided hot air duct section, the positioning of the inlet edge or the inlet area along a longitudinal axis of the heat exchanger parallel to the flow direction can be designed such that the temperature of the hot air at this position is still below the maximum permissible surface temperature, or below a lower limit temperature required by the vehicle manufacturer.

[0023] According to exemplary embodiments, the heat exchanger is provided to have a base body and a plurality of ribs that are essentially parallel to each other in the flow direction and preferably extend integrally outwards from the base body.

[0024] Further embodiments may provide that, in the air heater, the separating element rests on contact surfaces formed by a small number of fins, so that the inner heating air duct section is essentially divided into corresponding finned channels, each bounded by adjacent fins, the separating element, and the outer wall of the heat exchanger's base body. Since the separating element rests on these contact surfaces, the fins no longer extend into the outer heating air duct section.

[0025] A further preferred refinement may involve recessing the outer edges of the fins in the section for receiving the partition element compared to their design in the undivided hot air duct section. This means that the height of the outer edge, which provides a bearing surface or a receptacle for the partition element, is lower above an outer surface of the (solid) base body of the heat exchanger compared to the corresponding height in the undivided hot air duct section. This measure leaves more space above (towards the outer casing) the fins and the partition element for the outer hot air duct section.

[0026] A further development of the air heater provides that the heat-generating assembly includes an evaporator with a combustion chamber, making the air heater a burner-based / fuel-based air heater. This means that the heat-generating assembly is preferably a burner assembly comprising an evaporator and a combustion chamber, i.e., designed as an evaporator burner. The burner assembly may preferably include further elements, such as a glow plug. In this case, the intake opening, the heat exchanger, and the outlet opening can essentially define a longitudinal direction along a longitudinal axis of the air heater that is parallel to the flow direction. With such a design, it is particularly advantageous that the separating element forms a cap and encloses or covers a longitudinally rearward region of the heat exchanger within the outer casing.Such a cap can also be described as a cooling cap due to its effect on the external temperature of the outer casing. One advantage is that with this design, the maximum temperatures are achieved precisely in the rear section of the heat exchanger. This is not only because the heated air has already traveled the longest distance past the heat exchanger here (with the result that it has cumulatively absorbed the greatest amount of heat).This is also because, as described earlier, the impact flow of the combustion gases within the heat exchanger leads to maximum heat transfer at a rear wall of the heat exchanger, and the flow in the hot air duct is also redirected in the rear area to guide the hot air around the back of the heat exchanger towards the central longitudinal axis, where the outlet opening is located in the axial configuration. This results in an impact flow with increased heat transfer to the outer casing. In other words, the cap encloses the area of ​​the heat exchanger that, without a separating element or cap, would lead to the maximum temperatures on an outer surface of the casing. The cap compensates for this effect and achieves a uniform temperature distribution across the outer surface of the casing.

[0027] Another advantage of designing the separating element as a cap is that instead of requiring several individual separating elements, a single, uniform component can be provided, thus reducing the number of parts.

[0028] Another advantage of the cap is that it can be used as an optional component in series production. For example, a more cost-effective version of an air heater with reduced heating output can be manufactured and offered without the cooling cap, while otherwise maintaining the same geometry, particularly of the heat exchanger. This eliminates the need to modify the heat exchanger geometry for this version.

[0029] A further development of the aspect in which the separating element is designed as a cap provides for defining an outlet area in the cap in the area of ​​the outlet opening of the outer housing, in which the partial flows of the heated air, which are separated during operation by the separating element into the inner heating air duct section and the outer heating air duct section, are brought together again before being discharged.

[0030] According to another embodiment, the heat exchanger is a counterflow heat exchanger in which, during operation, hot combustion gases impinge as an impact flow on a wall in a longitudinally rear region of the heat exchanger, are deflected laterally, and discharged in the opposite direction, with the heat exchanger reaching its maximum temperature in this rear region during operation. The advantages have already been mentioned above.

[0031] According to another embodiment, the separating element has a longitudinal length such that the amount of heat absorbed by the heat exchanger in the heated air during operation intended for the air heater, up to the point where it enters the outer section of the heated air duct, results in a temperature compatible with the limit values ​​specified in ECE R-122. The advantages arising from this have already been explained above.

[0032] Not only, but especially when the separating element is designed as a cap, it is advantageous to arrange an overheating temperature sensor in the outer and / or inner section of the hot air duct. Other temperature-sensitive components can also be located in the outer section of the hot air duct, i.e., between the cap and the outer housing or housing shell, where they are better protected.

[0033] Further embodiments relate to the separating element: it can be made of a metallic material, preferably the same material as the heat exchanger, and more preferably aluminum. This increases the service life in view of the expected temperatures. With the same materials used for the cap and the heat exchanger, the coefficients of thermal expansion are also matched, and thermally induced mechanical stresses are easier to manage. Regarding the fastening, the cap is connected to the heat exchanger by means of a clip connection. For this purpose, openings can be provided in the cap, into which cams on the heat exchanger engage. Furthermore, the heat exchanger can have a small number of contact points on which the cap can rest. The surface contact between the cap and the heat exchanger is kept to a minimum to reduce heat conduction.During manufacturing / assembly, the cap can simply be slid onto the heat exchanger from the front.

[0034] In such an embodiment, the separating element can be a component manufactured using a deep-drawing or pressing process, preferably as an aluminum sheet. This allows for cost-effective production.

[0035] Alternatively, the separating element can also be made of a high-performance plastic.

[0036] Another embodiment provides that the separating element is held at a distance from the outer housing by one or more insulating pads. This reduces heat transfer to the outer housing when the outer housing is mechanically held or supported by the cap. In addition to being placed on the separating element, the insulating pads can also be positioned in or on the housing shell.

[0037] It should be noted that, according to aspects of the invention, due to the reduction of convective heat transfer from the heat exchanger to the outer casing by using the cooling cap, the permissible surface temperatures can still be maintained, especially in undesirable malfunctions, such as overheating due to blockage of the intake opening, with appropriate design.

[0038] In the aspects of the invention proposed here, the separation of the heating air flow into partial flows can, on the one hand, reduce the convective heat transfer to the outer casing or casing shell in the area of ​​high heating air temperatures, and on the other hand, reduce the heating air temperature itself near the wall. The surface temperatures of the outer casing or of one or more of the respective casing shells can thus be effectively reduced with only a slight additional pressure drop. Brief description of the drawings:

[0039] The invention is explained below by way of example with reference to the following figures.

[0040] They show: Fig. 1. A schematic longitudinal section provides an overview of a conventional power- or fuel-operated air heater; Fig. 2 in longitudinal section view an overview of a power- or fuel-operated air heater according to an exemplary embodiment; Fig. 3 a perspective view of the air heater from Fig. 2, with the rear housing shell removed; Fig. 4A, B the separating element of the air heater designed as a cap made of Fig. 3 in two different versions (with and without isolator pads); Fig. 5. Remove the heat exchanger of the air heater. Fig. 3 with cap turned up in perspective view; Fig. 6 how Fig. 5, but in side view. Detailed description of preferred embodiments:

[0041] In the following description of the drawings, identical reference numerals denote identical or comparable components. The features of the invention disclosed in the preceding description, in the drawings, and in the claims can be essential for the realization of the invention, both individually and in any combination.

[0042] The Fig. Figure 1 shows a schematic longitudinal section overview of a conventional fuel-operated air heater 100. The air heater 100 is intended, for example, for use in a motor vehicle. The air heater 100 has an outer housing G with an intake opening 11 for heated air and an outlet opening 12 for the heated air. A combustion chamber housing 36 with a fuel-operated combustion chamber 35 is located in a heat exchanger 30 of the air heater 100. A combustion air blower 31, designed as a side-channel blower (not shown in detail), provides the air supply (oxidizer) and airflow to the combustion chamber 35. The combustion air blower 31 is connected to a laterally arranged air inlet 33, from which it draws in the combustion air. Also not shown in detail are a fuel supply line, a vaporizer for the fuel, and an ignition device for starting a combustion process.In combustion chamber 35, the fuel and the combustion air containing the oxidizer are brought into chemical reaction to generate heat.

[0043] The heated air is drawn from the environment through the intake opening 11 at one end of the air heater 100 by means of a hot air blower 14 and exits, heated, through the outlet opening 12 at the rear of the air heater opposite the front, after flowing around the heat exchanger 30 in corresponding hot air channels 39. The intake opening 11 and the outlet opening 12 of the air heater 100 are shown, purely by way of example, to lie on a common longitudinal axis M of the heat exchanger 30 and the combustion chamber 35, along which the air flows through the air heater 100. The combustion air blower 31 and the hot air blower 14 are both driven by a drive motor 20', which is controlled by a control device 18' in a known manner, in particular depending on the required heating output.

[0044] On one exhaust gas side of the heat exchanger 30, after combustion in the combustion chamber 35, hot combustion gases flow as an impact flow 22 along the longitudinal axis M against a wall in a longitudinally rearward region B of the heat exchanger. Fig. Figure 1 shows the combustion chamber 35 in a purely schematic representation, and a flame tube, typically tapered in the direction of flow, can be connected to it. After leaving the combustion chamber or flame tube and the impact flow against the wall of the heat exchanger, the combustion gases are sharply deflected by 180° and then flow through the heat exchanger 30 in the opposite direction 23 to the flow direction 23 towards the exhaust gas outlet 34. A heat exchanger constructed in this way can also be referred to as a counterflow heat exchanger. Due to the high flow velocities and the sharp deflection of the flow, an impact flow 22 with very high heat transfer to this wall forms on the exhaust gas side in the rear region B of the heat exchanger 30.

[0045] The exhaust gases are discharged through flow channels 37, which are formed by fins (not shown) projecting inwards from an inner surface of the heat exchanger 30 and extending along the longitudinal axis M to improve heat transfer. Due to this design, the heat exchanger 30 reaches a maximum temperature in the rear region B during operation, which decreases from back to front as heat transfer progresses along the flow channels 37. Accordingly, the heated air reaches its highest temperatures in the heated air channels 39 near the rear region B before being discharged from the outlet opening 12. This discharge opening then transfers its heat to the outer casing G. However, due to the comparatively low power densities of conventional air heaters, the air heater 100 can achieve surface temperatures on the outer casing G that are still within the permissible range defined by the legislator in the ECE R-122 regulation.

[0046] The Fig. Figure 2 shows a fuel-based air heater 1 according to an embodiment that is significantly more compact than the one in Fig. 1 and therefore exhibits an increased power density. Some differences are described below, for example, regarding... Fig. 1 is explained, while reference is made to the description above regarding matching features. The air heater 1 has an outer housing G constructed from two housing shells. In the Fig. Figure 3 shows the front housing shell G1, while the rear housing shell G2 has been removed, revealing a corresponding heat exchanger 30. The front housing shell G1 has an intake opening 11 and the rear housing shell G2 has an outlet opening 12, between which the hot air duct(s) 39 extend. A hot air blower 14, driven by a drive motor 20, ensures the flow of hot air through the hot air duct(s) 39. The drive motor 20 is controlled by a control device 18 in a known manner, similar to the procedure described above.

[0047] The outer casing G accommodates the aforementioned components as well as the heat exchanger 30, as shown in Fig. Figure 2 shows the heat exchanger 30, which comprises a substantially cylindrical base body 26 with a rear wall B. Radially outward from an equally spaced outer wall 29 of the base body 26, ribs 25 extend circumferentially. The heat exchanger 30 exhibits overall axial symmetry, defining a longitudinal axis M which, in the exemplary embodiment, also extends through the intake opening 11 and the outlet opening 12. A direction R parallel to the longitudinal axis M is defined from the intake opening 11 to the outlet opening 12, which essentially coincides with the flow direction 49 in the heating air channel(s).

[0048] The heat exchanger 30 has an interior that opens in the opposite direction to R and accommodates a combustion chamber housing 36 with a fuel-operated combustion chamber 35. A combustion air blower 31, designed as a side-channel blower and driven by the same drive motor 20, provides the air supply (oxidizer) and airflow to the combustion chamber 35. The combustion air blower 31 is connected to a laterally arranged air inlet 33, from which it draws in the combustion air during operation. Also not shown in detail are a fuel supply line, a vaporizer 38 for the fuel, and an ignition device for initiating combustion. In the combustion chamber 35, the fuel and the combustion air containing the oxidizer undergo a chemical reaction to generate heat.

[0049] After leaving the combustion chamber or a flame tube (not shown in detail) and the impact flow against the rear wall of the heat exchanger 30, the combustion gases are sharply deflected by 180° and then flow in the opposite direction 23 to the flow direction 49 of the heating air on the outside of the heat exchanger 30 in flow channels 37 formed by internal ribs (not shown in detail) to the exhaust gas outlet 34 through the heat exchanger 30 and are released there.

[0050] As in Fig. As can be clearly seen in Figure 2, the heated air flows in the heated air duct 39 in the direction of flow 49 in a section 42, the interior of which, viewed radially away from the longitudinal axis M, is defined between the outer wall 29 of the base body 26 of the heat exchanger 30 and an inner wall 70 of the outer casing G (or the front casing shell G2), but extends in a circumferential direction around the heat exchanger 30.

[0051] As in the perspective view of the Fig. As can be seen more clearly in Figure 3, where the rear housing shell G2 has been removed, a separating element 50, designed as a cap 51, is placed on a rear end of the heat exchanger. The separating element 50 extends circumferentially around the heat exchanger 30 and follows the outer contour formed by its fins 25. Furthermore, due to its shape, the cap 51 also covers part of the rear area B of the heat exchanger 30. The cap 51 has a length L along its longitudinal axis M. Over this length L, an inner hot air duct section 52 is formed between the separating element 50 (more precisely: an inner surface of the separating element 50) and the outer wall 29 of the base body 26 of the heat exchanger 30. This inner hot air duct section 52 is further subdivided by the fins 25. However, the cap 51, or rather theThe separating element 50 does not contact every fin 25, but preferably only touches the heat exchanger at a small number of contact surfaces or points in order to limit heat transfer to the separating element 50 by thermal conduction. Thus, the fin channels formed by the subdivision are interconnected and together form the inner hot air duct section 52. In the exemplary embodiment, the separating element 50, like the heat exchanger 30, is made of aluminum.

[0052] Again Fig. As can be seen from Figure 2, the separating element 50 is located within the outer housing G or the front housing shell G2, but spaced apart from it to form an outer hot air duct section 54 between an outer surface of the cap 51 or the separating element 50 and the inner wall 70 of the outer housing G. This outer hot air duct section 54 is not divided by ribs. The inner hot air duct section 52 and the outer hot air duct section 54 are separated from each other by the separating element 50. Both sections have a length L measured along the longitudinal axis M (a in Fig. (Ignoring the visible deflection towards the longitudinal axis M at the rear end of the heat exchanger).

[0053] A section of the heat exchanger 30 exceeding the length L is formed by the section 42 described above, which is not subdivided in the radial direction. Between the single-piece section 42 on the one hand and the inner and outer heating air duct sections 52, 54 on the other, there is thus an inlet area 56, which is formed by an inlet edge of the separating element 50. At this point, the heating air flow is divided into two parallel partial flows: an outer heating air flow and an inner heating air flow.

[0054] Over its length L, the inner hot air flow from the base body 26 and the fins 25 absorbs significantly more heat than the outer hot air flow from the separating element. Therefore, the outer hot air flow reaches a slightly lower temperature than the inner hot air flow. Accordingly, during operation, the temperature of the outer housing G, particularly at the rear end of the air heater 1, is also significantly lower compared to a case where the separating element 50 is not present, despite an otherwise identical design. An overheating sensor or a temperature sensor (neither shown in the figures) can be arranged in the inner hot air duct section 52 or the outer hot air duct section 54 (or in both).

[0055] The separating element 50 has essentially perpendicular side surfaces 50a, 50b, 50c, and 50d to form the cap shape 4, as well as an end surface 50e in which a circular opening is formed. When installed, this opening forms a central outlet area 60. The position of this opening corresponds to the outlet opening 12 of the outer housing. The end surface 50e follows the outer contour of the rear area B of the heat exchanger 30 and thus extends the inner and outer hot air channels 52, 54 formed by the side surfaces 50a, 50b, 50c, and 50d to the outlet area 60. In this section, the hot air flow is deflected inwards towards the outlet opening 12.

[0056] The one in Fig. The cap 51 or the separating element 50 shown in Figure 3 can be provided with insulator pads 62 on the outer edges of the cuboid profile. These pads can come into mechanical contact with the outer housing G or the front housing shell G2. The insulator pads 62 are made of a heat-resistant material with low thermal conductivity. The insulator pads 62 serve as contact points only in exceptional cases. Within the nominal dimensions and tolerances, the heat exchanger 30 or the separating element 50 does not touch the housing shells G1, G2 without exerting a significant external force on the housing shells.However, in order to absorb potentially excessive forces from the respective application, the insulator pads 62 are positioned so that the heat exchanger 30 always initially comes into contact only with one of the insulator pads 62 in any position, instead of touching the corresponding housing shell G1, G2 and thus introducing excessively high temperatures into the housing shells G1, G2.

[0057] The Fig. Figure 4B shows the corresponding cap 51 (here designated with the reference numeral 51b for differentiation) in a state prior to assembly on the heat exchanger 30. A preferred and in Fig. The embodiment shown in Figure 4A does not provide for the installation of insulator pads on the cap 51 (in Fig. 4A (designated with reference numeral 51a). This alternative embodiment of an air heater 1 is shown in the perspective partial view of the Fig. 5 and the side view of the Fig. Figure 6 shows, but only the heat exchanger 30 with attached cap 51 is shown there, without the outer casing G and other components. The two alternative separating elements 51a, 51b are shown, for example, in Fig. 2. Interchangeable without requiring modifications to other components. Both the heat exchanger 30 with the separating element 50 and the outer housing G or the front housing shell G2 can be attached directly or indirectly to a support component or frame element of the air heater 1 (not shown in detail in the figures) and therefore, as described, do not necessarily need to touch each other. In this embodiment, the elimination of dedicated contact points further reduces heat transfer from the separating element 50 to the outer housing G.

[0058] The separating element 50 or the cap 51 can be, as shown by Fig. As can be roughly discerned, the heat exchanger 30 is attached to it by means of two cams each (top and bottom), which engage in corresponding openings 64 on opposite side surfaces 50a, 50c of the cap 51. Simultaneously, three contact points are formed on each of the left and right sides of the heat exchanger 30, against which the cap 51 can rest via its opposite side surfaces 50b, 50d. This serves to keep the surface contact between the heat exchanger 30 and the cap 51 as low as possible in order to minimize heat conduction into the cap 51 or the separating element 50.

[0059] It should be noted that other modifications are also possible, particularly with regard to the separating element 50. For example, in the embodiments, the separating element is formed in one piece. However, according to modifications, it can also be formed in multiple parts. For example, the in Fig. The side surfaces 50a,b,c,d shown in Figure 4A can also be provided as individual elements. Furthermore, the separating element 50 can also be provided without a cap shape, by having only the side surfaces 50a,b,c,d, but not those shown in Figure 4A. Fig. 4A shown end face 50e. Reference symbol list 1 air heater 11 Intake opening (heating air) 12 Dispensing opening (heated air) 14 hot air blowers 18' Control device 20' drive motor 22 Impact flow 23 Flow direction (180 °C deflected combustion gases) 25 fins (on the outside of the heat exchanger) 26 Base body (heat exchanger) 29 Outer wall (base body of the heat exchanger) 30 heat exchangers 31 combustion air blowers 33 Air intake (combustion air) 34 Exhaust gas outlet 35 Combustion chamber 36 Combustion chamber housing 37 flow channels (combustion gases) 38 evaporators 39 Heated air duct Section 40 42 undivided heating air duct section 49 Flow direction 50 separating element 51 cap 52 inner heating air duct section 54 outer heating air duct section 56 Inlet area 60 Outlet area 62 insulator pads 70 Inner wall (outer casing) 100 Air heater (conventional) B rear area of ​​the heat exchanger G Outer casing M Longitudinal axis R Longitudinal direction

Claims

[1] Air heater (1), in particular fuel-based air heater, for a vehicle, comprising: a component assembly (35, 36) for generating heat; a heat exchanger (30) that thermally interacts with the assembly (35, 36); an outer housing (G) that accommodates the assembly (35, 36) and the heat exchanger (30), wherein the outer housing (G) and the heat exchanger (30) form at least one heating air duct (39) between them, formed by an inner wall (70) of the housing (G) and an outer wall (29) of the heat exchanger; a hot air blower (14) which is designed to draw in hot air via an intake opening (11) of the outer housing (G) and to convey it along a flow direction (49) through the at least one hot air duct (39), and to discharge the hot air via an output opening (12) of the outer housing (G); characterized by : a separating element (50) which is arranged in the at least one heating air duct (39) and extends in a section (40) of the heating air duct (39) along the flow direction (49) determined by the operation of the heating air blower (14), wherein the separating element (50) in this section (40) divides the hot air duct into an inner hot air duct section (52), which is defined between the separating element (50) and the outer wall (29) of the heat exchanger (30), and into an outer hot air duct section (54), which is defined between the separating element (50) and the inner wall (70) of the housing (G), so that the heated air flowing in the heated air duct (39) during operation is divided at an inlet area (56) into the two heated air duct sections (52, 54) into two parallel partial flows. [2] Air heater (1) according to claim 1, wherein both the inner heating air duct section (52) and the outer heating air duct section (54) are jointly connected on their side defining the inlet area (56) for heating air against the flow direction (49) of the heating air to an undivided heating air duct section (42) which extends continuously from the inner wall (70) of the outer casing (G) to the outer wall (29) of the heat exchanger (30). [3] Air heater (1) according to claim 1 or 2, wherein the heat exchanger (30) has a base body and a plurality of ribs (25) extending, preferably substantially parallel to each other, in the direction of flow (49) and outwards from the base body (26). [4] Air heater (1) according to claim 3, wherein the separating element (50) rests on contact points formed by at least a subset of the ribs (25), so that the inner heating air duct section (52) is essentially divided into corresponding rib channels, each bounded by adjacent ribs (25), the separating element (50) and the outer wall (29) of the base body (26) of the heat exchanger (30). [5] Air heater (1) according to claim 4, wherein outer edges of the ribs (25) in the section (40) for receiving the separating element (50) are set back compared to their design in the undivided heating air duct section (42). [6] Air heater (1) according to any one of claims 1 to 5, wherein the assembly (35, 36) for generating heat comprises an evaporator (38) with combustion chamber (35); the intake opening (11), the heat exchanger (30) and the outlet opening (12) essentially define a longitudinal direction (R) along a longitudinal axis (M) of the air heater (1) which is parallel to the flow direction (49); the separating element (50) forms a cap (51) overall and encloses a rear area (B) of the heat exchanger (30) within the outer casing (G) when viewed in the longitudinal direction (R). [7] Air heater (1) according to claim 6, wherein in the cap (51) in the area of ​​the outlet opening (12) of the outer housing (G) an outlet area (60) is defined in which the partial flows of the heating air which are separated during operation by the separating element (50) into the inner heating air duct section and the outer heating air duct section are brought together again before being discharged. [8] Air heater (1) according to one of claims 6 or 7, wherein the heat exchanger (30) is a counterflow heat exchanger in which, during operation, hot combustion gases as an impact flow (22) meet a wall in a rear region (B) of the heat exchanger (30) viewed in the longitudinal direction (R), are deflected laterally and discharged in the opposite direction, wherein the heat exchanger (30) assumes a maximum temperature in the rear region (B). [9] Air heater (1) according to one of claims 6 to 8, wherein an overheating temperature sensor is arranged in the outer and / or inner heating air duct section (54). [10] Air heater (1) according to any one of claims 6 to 9, wherein the separating element (50) is made of a metallic material, preferably of the same material as the heat exchanger, more preferably of aluminium. [11] Air heater (1) according to any one of claims 6 to 10, wherein the separating element (50) is a component manufactured by a deep drawing or pressing process, preferably as aluminium sheet. [12] Air heater (1) according to one of claims 6 to 11, wherein the separating element (50) is made of a high-performance plastic. [13] Air heater (1) according to one of claims 6 to 12, wherein the separating element (50) is held at a distance from the outer housing (G) by one or more insulator pads.

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