ELECTRIC HEATING DEVICE

Description

[0001] The present invention relates to an electric heating device with a housing that forms a heating element receptacle, typically holding a PTC element under preload, and at least one fluid channel. The PTC heating element has a press-fit profile adapted for insertion into the heating element receptacle and forming a PTC receptacle. This PTC receptacle contains at least one PTC element, electrically conductive conductor tracks adjacent to it, and optionally, insulation that provides insulation and supports the conductor tracks against the heating element receptacle. This optional insulation can be provided if—as is probably more common—the press-fit profile itself is made of a metal and thus an electrically conductive material.

[0002] According to the present invention, the housing components are to be potential-free, i.e., not used for conducting the power current.

[0003] An electric heating device with the features of claim 1 is known, for example, from EP 2 637 474 A1 and EP 2 337 425 A1. In this prior art, the housing is provided with a U-shaped receiving pocket that forms the heating element receptacle and in which a profile is provided that is pressed into the receiving pocket and accommodates at least one PTC element. The solution described in EP 2 337 425 A1 discloses a conductor track, consisting of a sheet metal piece, abutting a main side surface of the PTC element, with contact projections bent out of the plane of the sheet metal piece. These projections serve only to improve electrical contact, but not to clamp the element.In the current state of the art, pre-tensioning is achieved using a wedge element which is pressed into the receiving pocket in order to position the heat-generating layers, possibly with insulation in between, as thermally conductive as possible against the inner surfaces of the heating element receptacle, thus ensuring good heat dissipation on the one hand, and on the other hand reliably electrically contacting the conductor tracks with the PTC element.

[0004] A PTC element is a semiconducting ceramic component with self-regulating properties. As it heats up, its electrical resistance increases. This reduces the PTC element's ability to absorb electrical power and convert it into heat. Therefore, good thermal contact with the PTC element is essential for efficient heat dissipation.

[0005] There has been no shortage of proposals in the past for meeting the diverse requirements of an electric heating device. The electric heating device according to the present invention is used particularly in motor vehicles. Here, special conditions apply that the electric heating device must satisfy. Firstly, the electric heating device must be designed to be as lightweight as possible. Secondly, it must be able to withstand the conditions within a motor vehicle. For example, the electric heating device must be able to withstand the vibrations in a motor vehicle over the long term and remain operational for years. Finally, scalability of the design is also required nowadays, so that the electric heating device can be easily adapted to different models and equipment variants.The electric heating device according to the present invention can be used as the sole heater, for example, in an electric vehicle. This electric heating device heats at least the interior, and optionally also components of the electric vehicle's drive system. However, the electric heating device can also be used as an auxiliary heater in a vehicle with an internal combustion engine, whose coolant is routed via a heat exchanger and used for air conditioning the vehicle interior. It is understood that the electric heating device is not operated continuously. Therefore, the electric heating device is also subject to temperature fluctuations, which lead to varying states of expansion and stress within the device.These are accompanied by dimensional changes in the design of the electric heating device, which, in any case, must not lead to a loss of good electrical and thermal contact of the PTC element during the lifetime of the electric heating device in the case of the electric heating device according to the invention.

[0006] US 2021 / 033303 A1 relates to a generic electric heating device. DE 10 2019 211567 A1 and DE 10 2018 221654 A1 each relate to sheets with projections that are to be arranged between a PTC element and a housing around the PTC element in order to apply a preload to the PTC element. EP 0 899 985 A1 relates to a housing of an electric heating device made of extruded profiles.

[0007] The present invention aims to provide an electric heating device of the type mentioned above, which meets the above requirements in an improved manner. The electric heating device according to the invention is intended to enable good heat extraction from the PTC element with reduced manufacturing and assembly effort.

[0008] To solve this problem, the present invention proposes an electric heating device with the features of claim 1. This device has, in a manner known per se, at least one PTC element and electrically conductive conductor tracks, typically in the form of sheet metal strips, adjacent to it. The heating cell thus formed, optionally surrounded by insulation, is provided in a press-fit profile. The press-fit profile is generally a cylindrical, uniform component. The press-fit profile can be made of a ceramic material. In this case, insulation can be omitted. However, the press-fit profile is usually made of a metal. The press-fit profile is preferably manufactured as an extruded profile and cut to length.

[0009] Similarly, the housing of the electric heating device according to the invention is formed as an extruded profile and cut to length. It is possible to combine several such housings in the electric heating device, thus enabling easy adaptation to the desired heating output and therefore to different vehicle types and equipment.

[0010] The press-fit profile and the housing have deformation projections located in the heating element receptacle, and thus between the housing and the press-fit profile. These deformation projections hold the press-fit profile under preload within the heating element receptacle. The preload is such that the PTC element and the conductor tracks, and any insulation, are held within the PTC receptacle in a position where these layers are in good thermal conductivity against each other, at least with respect to the main faces of the PTC element. The main faces of the PTC element are the largest surfaces of the element. The element is typically cuboid in shape. The main faces are parallel to each other. The other surfaces usually form a circumferential border that connects the two main faces.

[0011] The electrical heating device according to the invention preferably has two extruded profiles. One extruded profile forms the housing. The other extruded profile forms the press-fit profile. Deformation projections are provided between the two extruded profiles. These deformation projections also typically extend in the direction of the profiles. When the press-fit profile is inserted into the heating element receptacle of the housing, the deformation projections are deformed. The deformation can be plastic and / or elastic. Due to the deformation, a solid thermally conductive and electrical connection is formed between the PTC element, the conductor tracks abutting the main side surfaces, and the opposing inner surface of the PTC receptacle, optionally with insulation in between.

[0012] Depending on the length of the extruded profile, several PTC elements can be arranged in series. The length of the extruded profile can be cut to any desired length. This allows the electrical heating device to be adapted to the required heating power simply by changing the length of the housing. The PTC elements are arranged evenly along the length of the extruded profile. As is generally known in the art, the PTC elements can be housed in a positioning frame that extends essentially between the two conductor tracks and forms recesses for the PTC elements, offset from one another along the length of the extruded profile.

[0013] To ensure uniform heat dissipation from the at least one PTC element, the housing incorporates several fluid channels extending parallel to one another. The at least one heating element receptacle is located between at least two fluid channels. It has proven advantageous to provide at least two, preferably four, fluid channels on both sides of the heating element receptacle. An even number of fluid channels is preferred because the fluid is typically introduced at one end face of the housing and simply redirected on the opposite side. Flow guidance is simpler if the fluid is transferred beyond a heating element receptacle and perpendicular to its extension on the fluid inlet side. This allows for a relatively simple cover on the opposite side of the housing.

[0014] Opposite such a cover, which typically deflects the flow from one fluid channel of the housing to the other, a connection housing is preferably provided that connects one of the fluid channels to an inlet opening for the fluid to be heated and the other of the fluid channels to an outlet opening for the fluid to be heated. It is understood that the housing can form a plurality of fluid channels, each connected in series by deflecting the flow at the end faces of the extruded profile and connected to the inlet and outlet openings only at their beginning and end, respectively.However, fluid channels can also be connected in parallel to each other, which has the advantage of a higher temperature difference between the heating temperature of the PTC element and the temperature of the fluid, and thus more effective heat transfer, but the disadvantage of a potentially lower final temperature of the fluid heated in the electrical heating device.

[0015] The parallel fluid channels communicating with each other on the front face of the housing are preferably surrounded by a channel seal that seals the adjacent fluid channels against the cover or connection housing. This channel seal typically surrounds only two directly communicating fluid channels. These fluid channels preferably communicate through a recess that is cut into the front face of the housing. This allows the cover or connection housing to fit tightly against the housing without compromising sufficient flow between the adjacent fluid channels.

[0016] Opposite this recess, a power transistor / IGBT is preferably provided on the side of the terminal housing, which is in thermally conductive contact with the terminal housing. In this way, the fluid flow deflected in the area of ​​the recess can cool the power transistor. If the terminal housing is made of metal, insulation, for example in the form of Kapton film, is located between the power transistor and the inner surface of the terminal housing. The power transistor is usually directly connected to a printed circuit board, as illustrated in an embodiment of a control device according to the present invention.

[0017] Preferably, a heating element seal is provided between the housing and the connection housing, sealingly enclosing the heating element receptacle. Thus, the heating element receptacle preferably has a separate seal. It is understood that the heating element seal and the adjacent channel seal may be identical in certain sections. Preferably, a single sealing element is located on the end face of the housing, between the housing and the cover or the connection housing. Within an area surrounded by the heating element seal, the connection housing has at least one through-hole. At least one contact tongue passes through this through-hole and is electrically connected to one of the conductor tracks of the associated PTC heating element. The corresponding contact tongues project into the connection housing and are electrically connected there.The connection is preferably made via a printed circuit board (PCB) that can group various PTC heating elements into heating circuits and / or is additionally populated with components, so that this PCB can form a control unit within the meaning of the present invention. However, the populated PCB can also be located on a different layer than the PCB that electrically connects the contact tongues and is not populated with electronic components.

[0018] Other sealing methods are conceivable. For example, the housing can be materially bonded to the connection housing, in particular by welding, soldering or gluing.

[0019] According to a preferred embodiment of the present invention, the electric heating device is provided as a single unit with a control unit. This control unit is typically integrated into the terminal housing. The control unit serves to control the at least one PTC heating element. The PTC elements, which are provided in a single press-fit profile, are usually assigned to one heating circuit. However, several PTC heating elements arranged in parallel can be assigned to different heating circuits and switched via the control unit. In this preferred embodiment, the conductor tracks extend beyond the end of the housing and are extended into the terminal housing. The conductor tracks are electrically connected to the control unit. The terminal housing is typically divided into a fluid-carrying flow channel area and an electrical connection area for the conductor tracks that accommodates the control unit.The connection area is typically located on the side of the flow channel facing away from the housing and is closed off with a cover. The conductor tracks therefore extend through the flow channel. The connection housing usually forms channels in which the conductor tracks are guided, separate from the fluid, through the flow channel and into the connection area.

[0020] With regard to the desired preload towards the main side faces of the PTC element, the aforementioned deformation projections are regularly, and usually exclusively, provided between the main side faces of the PTC element and the opposite inner surface of the heating element receptacle. To ensure uniform, bilateral preload, corresponding deformation projections are provided between each main side face of the PTC element and the opposite inner surface of the heating element receptacle. The deformation projections typically extend across the entire width of the PTC element, the heating element receptacle, and the press-fit profile. The width extends transversely to the longitudinal direction of the housing as an extruded profile, i.e., transversely to the pressing or extrusion direction during the manufacturing of the extruded profile. The height extends in the plane of the width as a third Cartesian direction.The main side surface of the PTC element lies in a plane containing the width and length directions.

[0021] With a view to achieving the most symmetrical heat extraction possible and a uniform tolerance compensation, a preferred embodiment of the present invention proposes to provide a plurality of deformation projections between one of the main side surfaces of the PTC element and the opposite inner surface of the heating element receptacle.

[0022] With a view to good heat transfer between the press-fit profile and the inside of the heating element receptacle, a preferred embodiment of the present invention proposes that the deformation projections be designed as interlocking tongue-and-groove elements, wherein a groove-limiting projection and / or at least a spring projection forming at least part of the spring is pivotable about an axis extending in the insertion or longitudinal direction. According to this embodiment, the tongue-and-groove elements overlap considerably in the vertical direction and are in contact with each other in the vertical direction. This creates a solid, large-area heat transfer path between the housing and the press-fit profile. At least one groove-limiting projection and / or at least one spring projection forming at least part of the spring are preferably wedge-shaped towards their free end.The wedge shape promotes the elastic pivoting movement of at least one of the deformation projections during joining. The present invention assumes that the heating element receptacle extends in the longitudinal direction of the housing and that the deformation projections, i.e., the tongue-and-groove elements, extend in this direction. The joining movement is thus achieved by inserting the press-fit profile longitudinally into the housing.

[0023] According to a preferred embodiment of the present invention, at least one compression element is provided between the press-fit profile part and a main side surface of the PTC element. The compression element is typically located within the press-fit profile part and provides additional preload to the components within the PTC receptacle, optionally also to equalize the preload force so that it is transferred uniformly to insulation and / or the PTC element. This prevents local overloading, for example, of a ceramic insulating plate and / or the ceramic PTC element. The compression element can be formed by a spring made of metal. The spring typically extends across the entire surface of the main side surfaces in the width direction.The compression element is preferably provided between an inner surface of the PTC receptacle and an insulating layer that covers the PTC element on the outside.

[0024] According to a preferred embodiment of the present invention, a curing adhesive is introduced into the heating element receptacle. This adhesive can fill any remaining gaps between the deformation projections and thus improve heat conduction. For this purpose, the adhesive can be a plastic adhesive with good thermal conductivity. It can, for example, be a silicone adhesive to which highly thermally conductive particles, such as aluminum oxide particles, have been added. In addition to the preload provided by the deformation projections, the adhesive also secures the position of the press-fit profile within the heating element receptacle.

[0025] Further details, features and advantages of the present invention will become apparent from the following description of an exemplary embodiment in conjunction with the drawing. The drawing shows: Figure 1: A perspective exploded view of an embodiment of the present invention; Figure 1: flow path within the embodiment according to Figure 1 Figure 2 shows a perspective side view of a press-fit profile part of the embodiment according to Figure 1 Figure 3 shows a cross-sectional view through the press-fit profile part. Figure 2 upon insertion into the electric heating device after Figure 1 Figure 4 shows a sectional view according to Figure 3 for a variant of the press-fit profile part; Figure 5, an end view of the housing; Figure 6, a sectional view along line VI-VI as shown in Figure 5 and Figure 7 a sectional view along line VII-VII according to the illustration in Figure 5 .

[0026] The Figure 1 shows an electric heating device with a housing 2 that is provided between a cover 4 and a terminal housing 6.

[0027] The housing 2 has three parallel heating element receptacles 8 with a substantially rectangular cross-section and adjacent fluid channels 10. Four fluid channels are provided laterally to each heating element receptacle 8. The fluid channels 10a carry flow from the cover 4 towards the connection housing 6. The fluid channels 10b carry the fluid in the opposite direction.

[0028] Distributed around its circumference, the housing 2 has several mounting channels 12 in which threaded rods (not shown) or self-tapping screws are provided, via which the cover 4 is connected to the terminal housing 6, creating a sealing seal between the housing 2 and the cover 4. Alternatively, self-tapping screws can also be used to seal the cover 4 or the terminal housing 6 against the housing 2.

[0029] The solution according to the invention has the advantage that the sealing of the respective heating element receptacles 8 against a uniform housing 2 takes place.

[0030] The in Figure 1The upper and lower fluid channels 10 communicate with pipe sections of the cover 4, which are designed as inlet nozzles 14, outlet nozzles 18, and deflection nozzles 20, respectively. The deflection nozzles direct the fluid flowing in the fluid channels 10 beyond one of the heating element receptacles 8 and across it. An inlet opening 16 is formed at the free end of the inlet nozzle 14. An outlet opening 19 is formed at the free end of the outlet nozzle 18.

[0031] The circulation of the medium is described in detail according to Figure 1aThis is evident. The flow of fluid on the side of the connection housing 6 is also evident from this. The deflection on one plane of a heating element receptacle 8 usually takes place within the housing 2, so that the cover 4 or the connection housing 6 in this area simply rests against the housing 2 as a flat plate, sealed at its end face. The free ends of the fluid channels 10 terminate in a recess 22 in the housing 2.

[0032] The housing 2 is manufactured as an extruded profile and cut to length. The press-fit profile, designated with reference numeral 24, is formed to the corresponding length. A press-fit profile 24 is provided in each of the heating element receptacles 8.

[0033] The press-fit profile is in Figure 1Recognizably projected by contact tongues 26, which are formed in one piece on contact plates, forming conductive tracks 28 that are received in a PTC receptacle 30 and are electrically conductively in contact with PTC elements 32 of a PTC heating device 34. Details on this are in particular Figure 3 to be taken.

[0034] Reference numeral 36 designates an insulating layer that covers the conductor tracks 28 on the outside. A compression element 38 is located between this insulating layer 36, which is formed from a ceramic plate, and a main side surface of the PTC receptacle 30.

[0035] To insert the aforementioned components into the PTC receptacle 30, the press-fit profile 24 is formed from two profile sections 40 that are joined together. The profile sections 40 are typically identical and can therefore be cut from a single extruded profile. The profile sections 40 and the housing 2 can, for example, be made of aluminum.

[0036] Deformation projections in the form of groove limiting projections 42 protrude from opposite main side surfaces of the press-fit profile 24.

[0037] How especially Figure 3 As illustrated, a multitude of identically shaped grooves 44 are recessed on the outside of the profile parts 40 between paired groove limiting projections 42. The grooves 44 extend in the insertion direction of the heating element receptacle 8, which is located in Fig. 1marked with E and corresponding to the extrusion direction during the production of the extruded profile.

[0038] Spring projections 46 protrude from the inside of the heating element receptacle 8. These spring projections 46 are integrally formed on the housing 2, which is designed as an extruded profile. As shown in the cross-sectional view according to Figure 3 The spring projections 46 taper wedge-shaped towards their free ends. Similarly, the groove-limiting projections 42 also taper wedge-shaped towards their free ends. It is understood that only the surfaces of the groove-limiting projections 42 that define the groove 44 have this shape. To illustrate this, the following are shown in Figure 3 The spring protrusions 46 on the right side have been omitted.

[0039] At the in Figure 3In the illustrated embodiment, the press-fit profile 24 is first fitted with the PTC heating element 34 and the compression elements 38 during assembly. The pre-assembled unit is then inserted into the heating element receptacle 8. The spring projections 46 engage in their corresponding grooves 44. A comparison of the right and left sides reveals... Figure 3 Deformation is visible in the area of ​​the groove limit projections 42. This provides a certain degree of tolerance compensation. Additionally, the compression element 38 is deformed to compensate for tolerances. Ideally, after assembly, the compression element 38 rests essentially over its entire surface against both the inner surface of the PTC receptacle 30 and the outer surface of the insulating layer 36.

[0040] The compression element 38 can be made of aluminium, copper, copper beryllium or another material with good thermal conductivity capable of applying permanently elastic preload forces.

[0041] Remaining cavities in the heating element receptacle 8 can be filled with a highly thermally conductive material, for example a curing plastic compound filled with thermally conductive particles.

[0042] At the in Figure 4In the illustrated variant, the groove limiting projections 42 are connected to the remaining profile section 40 via a relatively thin web 48. This web 48 creates a pivot axis that extends essentially in the insertion direction E. In this embodiment, compression elements can be omitted. Adjacent groove limiting projections 42 for different grooves 44 are sufficiently spaced apart so that they can pivot about their pivot axis when the wedge-shaped spring projections 46 are inserted, without colliding with each other. This allows for considerable tolerance compensation. The positions of the PTC heating element 34 within the press-fit profile 24 are thereby pressed against the inner surface of the PTC receptacle 30 with good elastic tension, thus improving heat dissipation.

[0043] The Figure 4This also illustrates the warping of the inner surfaces of the PTC receptacle 30, such that in the cross-sectional view it forms a contact surface that is essentially point-like and longitudinally linear against the insulating layer 36. This deformation of the press-fit profile 24 causes an additional elastic prestress of the PTC element 32 in the PTC receptacle 30.

[0044] As the detailed description illustrates, the deformation projections, in the form of the groove limiting projections 42 and the spring projections 46, create an elastic preload between the housing 2 and the press-fit profile 24. This ensures good thermal conductivity of the PTC element against the layers of the PTC heating element 34. It also ensures good electrical contact between the conductor track 28 and the PTC element 32.

[0045] How Figure 1As can be clearly seen, the contact tongues 26 extend beyond the press-fit profile 24 at the end. These contact tongues 26 are electrically contacted in the terminal housing 6.

[0046] The front view of housing 2 according to Figure 5 Figure 1 illustrates a sealing element 50. This sealing element 50 forms a channel seal 50a that surrounds two adjacent fluid channels 10a at their ends, as well as a heating element seal 50b that surrounds a heating element receptacle 8. The channel seal 50a and the heating element seal 50b share wall sections that are located in Figure 5 extend vertically between the individual areas. The sealing element 50 rests against the flat end face of the housing 2. On the opposite side, either the cover 4 or the connection housing 6 rests against it. Figure 5 The sealing element 50 is shown in relation to the connection housing 6.

[0047] The sectional view according to Figure 6Figure 52 illustrates the thermally conductive arrangement of a power transistor 52, which is shown as part of a control unit 54 that also includes a printed circuit board 56. This power transistor 52 is in thermally conductive contact with a wall section of the terminal housing 6, which in this case is made of aluminum. A Kapton foil is provided as electrical insulation between the terminal housing 6 and the power transistor 52.

[0048] Reference numeral 60 designates self-tapping screws that pass through the connection housing 6 and are screwed into the respective mounting channel 12. These screws 60 clamp the sealing element 50 between the end face of the housing 2 and the connection housing 6.

[0049] In Figure 7The connection housing 6 shows recessed feedthrough openings 62, which are penetrated by the contact tongues 26, which are electrically contacted with the circuit board 56 and extend through it. Reference symbol list

[0050] 2 Housing 4 Cover 6 Connection housing 8 Heating element holder 10 Fluid channel 10a Fluid channel 10b Fluid channel 12 Mounting channel 14 Inlet nozzle 16 Inlet opening 18 Outlet nozzle 19 Outlet opening 20 Deflection nozzle 22 Recess 24 Press-fit profile 26 Contact tongue 28 Conductor track 30 PTC holder 32 PTC element 34 PTC heating element 36 Insulation layer 38 Compression element 40 Profile part 42 Groove limiting projection 44 Groove 46 Spring projection 48 Web 50 Sealing element 50a Channel seal 50b Heating element seal 52 Power transistor 54 Control unit 56 Circuit board 58 Kapton foil 60 Mounting screw 62 Feedthrough opening Insertion direction

Claims

1. Electric heating device with a housing (2), which forms a heating element receptacle (8) holding at least one PTC element (32) under pretension and at least one fluid channel (10), and a PTC heating assembly (34) with a press-fit profile (24) inserted into the heating element receptacle (8), which forms a PTC receptacle (30) in which the at least one PTC element (32), strip conductors (28) abutting thereon in an electrically conductive manner and, if appropriate, an insulation (36) supporting the strip conductors (28) in an insulated manner against the PTC receptacle are provided, wherein the housing (2) is formed from an extruded profile, characterized in that deformation projections (42, 46) are formed between the housing (2) and the press-fit profile (24) by the housing (2) and the press-fit profile (24), by means of which projections the press-fit profile (24) is held under a pretension in the heating element receptacle (8).

2. Electric heating device according to claim 1, characterized in that the housing (2) forms a plurality of fluid channels (10) extending parallel to each other and at least one heating element receptacle (8) extending between at least two fluid channels (10) parallel thereto.

3. Electric heating device according to claim 2, characterized in that the housing (2) is provided at an end face with a cover (4) through which the flow is deflected from one of the fluid channels (10) into another of the fluid channels (10), and in that the housing (2) is provided on the opposite side with a connection housing (6) which connects one of the fluid channels (10) to an inlet opening (16) for the fluid to be heated and the other of the fluid channels (10) to an outlet opening (19) for the fluid to be heated.

4. Electric heating device according to claim 3, characterized in that adjacent fluid channels (10a) are connected in series and are surrounded at the end face by a channel seal (50a) which seals off fluid channels (10a) from the cover (4) or connection housing (6).

5. Electric heating device according to claim 4, characterized in that the adjacent fluid channels (10a) communicate with each other through a trough (22) recessed on an end face of the housing (2).

6. Electric heating device according to one of claims 3 to 5, characterized in that a heating element seal (50b) is provided between the housing (2) and the connection housing (6) and sealingly encloses the heating element receptacle (8).

7. Electric heating device according to claim 6, characterized in that the connection housing (6) forms a lead-through opening (62) surrounded by the heating element seal (50b), through which contact tongues (26) electrically connected to the strip conductors (28) project into the connection housing (6).

8. Electric heating device according to one of claims 3 to 7, characterized in that the connection housing (6) surrounds a control device (52) for controlling the at least one PTC heating assembly (34), and in that the strip conductors (28) project beyond the end of the housing (2), are extended into the connection housing (6) and are electrically connected to the control device (52).

9. Electric heating device according to one of the preceding claims, characterized in that deformation projections (42, 46) are provided between each main side surface of the PTC element (32) and the opposite inner side of the PTC receptacle (30).

10. Electric heating device according to one of the preceding claims, characterized in that a plurality of deformation projections (42, 46) are provided between one of the main side surfaces of the PTC element (30) and the opposite inner surface of the heating element receptacle (8).

11. Electric heating device according to one of the preceding claims, characterized in that the deformation projections are configured as interlocking groove and spring elements (42, 46), in that at least one groove limiting projection (42) limiting the groove (44) and / or at least one spring projection (46) at least partially forming the spring can be pivoted about an axis extending in the insertion direction (E).

12. Electric heating device according to claim 11, characterized in that at least one groove limiting projection (42) limiting the groove (44) and / or at least one spring projection (46) at least partially forming the spring is configured to be wedge-shaped tapering towards its free end.