DE102017218899A1 - Electric heating device for a motor vehicle - Google Patents

Abstract

The present invention relates to an electric heating device for heating a medium, preferably either water or air. For heating the medium, one or a plurality of heating stages is provided which can be controlled separately. Each of the heating stages is equipped with at least one PTC heating element. In series with the PTC heating element, at least one additional heating element is connected in each heating stage. The further heating element is designed as an inductor and has to a wound in the form of a coil heating conductor. In this way, the inrush current of the PTC heating elements can be lowered and any resulting waste heat emitted to the medium to be heated. The fact that the coil of the inductance is formed of a heating element, it also contributes simultaneously to the heating of the medium. Thus, an efficient heating can be realized with little space.

Description

The present invention relates to an electrical heating device for a motor vehicle with a plurality of heating elements, in particular PTC heating elements.

Electric heaters are used in the motor vehicle, for example, as additional heater to supplement the heating of the vehicle interior and other components, which is primarily due to the heat of the engine, or to allow, for example, a heating at standstill of the vehicle.

Of particular importance are electrical heaters in vehicles with electric or hybrid drive, in which the drive unit of the motor vehicle emits no or no sufficient waste heat for heating or air conditioning of the vehicle. It is advantageous if a heating device for electric or hybrid vehicles is also suitable, in addition to the supply of the interior of the motor vehicle with the required heat and the required for the running processes in individual parts of the system motor vehicle or at least to provide these promotional heat, such Example for preheating the vehicle battery.

The heaters used in electric and hybrid vehicles are for an automotive high voltage range (above 60 volts, preferably several hundred volts, up to 500 volts, typically between 280 volts and 430 volts (eg, 300 volts or 380 volts)). provided because the vehicle batteries used provide such a vehicle electrical system voltage. The heating power of such high-voltage heaters is on the order of 3 to 6 kW (kilowatts), compared to an order of magnitude of 1 to 1.7 kW (eg 1.2 kW) for 12 volt auxiliary heaters for motor vehicles.

Resistance heating elements are used in electric heating devices in motor vehicles, in particular PTC (positive temperature coefficient) heating elements. PTC heating elements are self-regulating, as they show a higher resistance with increasing heating, and therefore allow a smaller amount of current to pass at the same voltage. Thus, the PTC elements heat up to a maximum of a defined temperature. The self-regulating properties of the PTC heating elements therefore prevent overheating. The surface temperature of a PTC element can not exceed a certain maximum surface temperature during operation with the specified operating voltage. This maximum surface temperature is indicative of a PTC heating element. The heat generated by the PTC elements is delivered to a fluid medium, in particular to an air flow or a water flow.

A typical resistance curve of a PTC heater as a function of temperature is in 1 played.

A PTC heating element, after being turned on and then heated, reaches a point of the PTC characteristic at which the PTC heating element has a minimum resistance Rmin. At this point, the maximum current flows through the PTC heating element, which is significantly increased compared to the current flow in normal operation.

Due to their flat design, PTC heating elements in the form of ceramic plates also have a capacitive inrush current.

For PTC heaters, this results in high inrush currents, which make the construction of such heaters more expensive and complicate operation in a motor vehicle electrical system.

The object of the invention is to provide an electric heater that avoids such inrush currents and allows efficient heating.

This is achieved with the features of claim 1.

An electric heater according to the invention for a motor vehicle has at least two electrical heating elements for heating a medium, which are electrically connected in series. At least one of the heating elements is a PTC heating element. The further heating element is a wound in the form of a coil heating conductor, which acts as an inductance.

It is the particular approach of the invention to connect in series with a PTC heating element an inductance which throttles the inrush current and at the same time also acts as a heating element. For this purpose, the inductance is constructed so that a heating wire is wound in the form of a coil. As a result, this component acts as a heater and at the same time as an inductance. It can therefore deliver the heat generated by the heating wire to the medium. At the same time, the heat generated by the inductance is also provided for heating the medium.

With the solution according to the invention, the inrush current can be kept low and the capacitive switch-on peak can be cut off. Due to the double use of the further heating element as an inductance and as a heating element, the required installation space for the heating can be kept small, since an inductance does not have to be provided separately.

Preferably, the heating device has a plurality of heating stages connected in parallel and individually controllable, wherein each of the heating stages comprises a series arrangement of at least one PTC heating element and an inductance of a coil conductor wound in the form of a coil.

Thus, the flexible adjustability of the heating power or connectability of heating stages known multistage electric heaters is maintained and the advantage of the invention is achieved for each heating stage. Each heating stage has a combination of at least one PTC heating element and an inductance of a heating conductor. The inrush current can thereby be reduced for each heating stage, and the heat of the inductance is additionally supplied to the medium together with the heat of the heating conductor.

Preferably, the series connection of a PTC heating element and a heating conductor wound in the form of a coil is additionally supplemented by a series-connected inductance, so that each heating stage has such an additional inductance. However, this additional inductance is not sufficient for the release of heat to the Medium formed.

In this way, the inductance of a heating stage is variably adjustable. For this purpose, a further inductance is added in each series connection of heating elements (i.e. However, this is not designed as a heating element, so no coil wound from a heating conductor. As a result, each heating stage contains at least two inductors. However, only a portion of the inductors connected in series with the PTC heating element (s) contribute to the heating of the medium, namely the inductance formed as a heating element. The inductive properties of a heating stage can thus be easily adapted, for example, when the inductance of the inductor formed as a heating element is insufficient.

Preferably, the further inductance, which does not contribute to the heating of the medium, is likewise provided in the heating device, namely within a control circuit arranged in the housing of the heating device,
Thus, the additional inductances for the individual heat levels can be easily integrated into the existing structure of the heater.

Preferably, the outer dimensions of the PTC heating elements and the heating elements designed as an inductance are the same. As a result, the electric heater can be equipped with PTC heating elements and heating elements designed as an inductance.

Further preferably, the heating elements are arranged in the electric heater in the form of a heating register. The heating register has a plurality of positions for arranging heating elements. Each of the positions alternatively allows the arrangement of a PTC heating element or a heating element designed as an inductance.

With heating elements and receiving positions, which are each independent of the type of heating element, ie PTC or inductance, a heater adapted to the respective requirements is particularly easy to produce. A heating register may consist of a layered construction of heating elements (and possibly also radiator elements). In another alternative, predefined positions are provided in the housing, to which a heating element (PTC or heating wire) can be inserted.

Preferably, the heating stages are controlled by a PWM (Pulse Width Modulation). This is in a simple way a continuous adjustment of the heating power possible.

The total heating power of a heating stage or the electric heating device is preferably provided in equal parts by the PTC heating elements and the inductors designed as a heating element. This is especially true when the heating elements, and especially the PTC heating element, work in the steady state, so the special switch-on (in particular the point Rmin on the resistance characteristic for PTC heating elements) have passed through. The total heating power includes the heating power of the PTC heating elements and the inductors designed as a heating element.

Preferably, the total heating power of the electric heater is provided to at least 70 percent of the PTC heating elements - in the steady state of the heating operation.

The electric heater can be used as an air heater with air as the medium to be heated, as well as a water heater with a liquid, e.g. Be formed as a water to be heated medium.

A heating device according to the invention can also be used for other tasks in the motor vehicle, for the provision of required process heat, for preheating or keeping warm important parts, such as battery.

In particular, the invention comprises a motor vehicle, preferably an electric or hybrid vehicle with an operating voltage in the automotive high-voltage range, with a correspondingly designed electrical heating device.

Further advantageous embodiments are the subject of the dependent claims.

• 1 eine typische Widerstandskurve eines PTC-Heizelements in Abhängigkeit von der Temperatur zeigt;
• 2 eine perspektivische Seitenansicht eines beispielhaften wärmeerzeugenden PTC-Heizelements in Explosionsdarstellung zeigt;
• 3a bis 3d perspektivische Ansichten des inneren Aufbaus einer beispielhaften Induktivität zeigen; die gleichzeitig als Heizelement wirkt,
• 4 einen Ausschnitt aus einem schematischen Querschnitt durch einen geschichteten Aufbau eines Heizregisters für einen Luftheizer zeigt;
• 5 eine Aufsicht auf einen beispielhaften Luftheizer mit einem Heizregister zeigt;
• 6 eine perspektivische Seitenansicht eines beispielhaften Wasserheizers mit einem Heizregister zeigt; und
• 7a bis 7c schematische Darstellungen beispielhafter Reihenschaltungen einer elektrischen Heizvorrichtung mit einer und einer Mehrzahl von Heizstufen zeigen.

In the following, the present invention will be explained with reference to preferred embodiments in conjunction with the accompanying drawings, in which:

• 1 shows a typical resistance curve of a PTC heating element as a function of the temperature;
• 2 shows a side perspective view of an exemplary heat generating PTC heating element in exploded view;
• 3a to 3d show perspective views of the internal structure of an exemplary inductance; which also acts as a heating element,
• 4 shows a section of a schematic cross section through a layered structure of a heater for an air heater;
• 5 a top view of an exemplary air heater with a heating register shows;
• 6 a side perspective view of an exemplary water heater with a heating register shows; and
• 7a to 7c show schematic representations of exemplary series connections of an electric heater with one and a plurality of heating stages.

The electric heaters use according to the invention a series connection with two different types of heating elements for each heating stage, namely on the one hand PTC heating elements and on the other hand, a (resistance) heating conductor which also acts as an inductance. Both types of heating elements are preferably prefabricated as heat-generating elements with predetermined dimensions, so that they can be used arbitrarily for the construction of the electric heater, namely interchangeable.

The electric heater includes a plurality of heat-generating elements of the same dimensions containing either PTC elements or a heating wire. In this way, the respective composition of an electric heater of PTC heating elements and heating elements with heating wire is arbitrarily configurable. The individual heat-generating elements are respectively connected in series (electrically) in the electrical heating device in such a way that a heating stage contains at least one PTC heating element and a heat-generating element with a heating wire (which is designed as an inductance).

The electric heating device preferably comprises not only a single heating stage, but a plurality of separately controllable heating stages. Each heating level can be switched on separately depending on the desired heating capacity. Additionally or alternatively, the heating power of each heating stage via a PWM (pulse width modulation) is set. The individual heating stages can be controlled with a time offset in order to keep the burden of the motor vehicle electrical system low.

An exemplary embodiment for a heat generating element with PTC elements is shown in FIG 2 played. The heat-generating element each comprises a flat tube 28 , which on the inside with a sleeve-shaped, ie cylindrical insulation 28.1 in the form of an insulating film, such as polyimide or Kapton lined. Inside the insulation 28.1 are contact sheets 28.2 . 28.3 taken in between PTC elements 28.4 absorb and immediately electrically conductive abut it. The insulation 28.1 may comprise an electrically insulating heat-resistant film, which may be coated on one or both sides with PTFE. The insulating film can be under pressure and heat with the inside of the flat tube 28 be welded, for example, during operation of the heater. The PTC elements 28.4 are provided with a metallization, which as a coating on the PTC elements 28.4 is applied.

Every contact sheet 28.2 ., 28.3 has a contact tongue formed integrally thereon by punching and bending 28.5 , On one side is the flat tube 28 through an end plug 28.6 made of plastic, sealing in the flat tube 28 or the insulation 28.1 is glued. On the opposite side is in the same way an end cap 28.7 provided, made of plastic and integrally formed thereon guide sleeves 28.8 for the respective reeds 28.5 ausformt. As can be seen, the contact tongues 28.5 bend around at the end and are located at about the middle height of the PCT elements 28.4 ,

As insulation against main side surfaces of the flat tube 28 it is also possible to provide insulating layers, for example ceramic plates, plastic films or ceramic plates coated with plastic film. The insulation is an electrical insulation, which should preferably have a good thermal conductivity of at least 20 W / (m K). The individual layers of the layer structure, consisting of the insulation 28.1 the contact sheets 28.2 . 28.3 as well as the PTC elements 28.4 are usually loose in the flat tube 28 inserted. Through the end cap 28.7 or the end plug 28.6 These elements are axially first within the flat tube 28 fixed.

The present invention is not on the in 2 Specifically shown and described here embodiment for a PTC heating element limited. 2 shows only one possible variant for the configuration of a PTC heating element for installation in a heating coil. Other variants are well known in the art.

An exemplary embodiment of a heat-generating element with a heating wire, which is designed as an inductance is in the 3a to 3d played. The heat generating element comprises an in 3d shown flat tube 30 which in its external dimensions is in the 2 shown flat tube 28 corresponds to the PTC heating element and can be used interchangeably with this. The flat tube 30 takes a carrier 31 on, which is made of an insulating material. Suitable carrier materials are materials with particularly good insulation properties and good heat resistance, such as artificial mica (mica). A possible design for the wearer 31 is in 3a shown.

On the carrier 31 is a heating conductor 32 wrapped as in 3b shown. As material for the heating conductor 32 come Heizleiterlegierungen with high temperature resistance and preferably over a wide temperature ranges approximately constant specific electrical resistance (for example, constantan) into consideration.

The length of the heating conductor 32 depends on the required inductive properties and the heat output to be provided. Here is the heating conductor 32 in the form of a helix or double helix, possibly also in several layers around the carrier 31 wound.

In the in 3 shown embodiment are at one end in the longitudinal direction of the support contact tongues 33 shown, over which the heating conductor 32 is contacted electrically. Also the reeds 33 are preferably corresponding to those of the PTC heating element 2 designed so that both heating elements are used interchangeably in the electric heater. These can be the ends of the flat tube 28 for example according to 2 with a stopper 28.6 or an end cap 28.7 be closed, which for the electrical contacting guide sleeves 28.8 exhibiting.

In 3c is an external isolation 35 of the carrier 31 with the wound heating conductor 32 shown. The isolation 35 should be particularly heat resistant and have good thermal conductivity. As a material, for example, also art mica (micanite) into consideration.

The carrier 31 with the wound heating conductor 32 and the isolation 35 is in the flatroaster 30 pushed in, the flat tube 28 corresponds to that in 2 described in connection with the PTC heating element. By a corresponding end cap or an end plug as in connection with 2 described, the coil is made of heating wire 32 axially within the flat tube 28 fixable.

The present invention is by no means limited to that in 3 specifically shown and limited embodiment described here. 3 shows only one possible variant for the design of a heating element as Induktivtät, in which a heating element is used in the form of a coil for heating and for heat generation.

The heating elements, with PTC elements or heating wire, are preferably arranged in the electric heating device in the form of a heating register. A schematic example of a structure of a heater for air heaters is in 4 played. The heating register 40 consists of a layered construction of heating elements 41 . 42 and radiator elements 43 , In addition, further layers such as contact sheets, electrical insulation layers, etc. may be provided. The layered structure is traversed by air in a direction perpendicular to the image surface.

In the in 4 shown construction are between radiator elements 43 heating elements 41 . 42 arranged. In the layers with heating elements 41 . 42 are either PTC heating elements 41 or heating element heating elements 42 intended. Preferably, the types of heat generating elements (ie either PTC or heat conductors with inductive properties) alternate in successive layers with radiator elements for dissipating the heat to the medium flowing through.

The two in 4 For example, shown heating elements are part of the same heating stage and electrically connected in series.

As previously stated, the heating elements 41 . 42 in their dimensions and their contacts preferably the same design, so that they arbitrarily in the register 40 can be used.

The representation in 4 only shows a section of a heating register in a schematic manner. In addition, additional layers of heating elements 41 . 42 and radiator elements may be provided which correspond, for example, additional heat levels.

In a water heater, the heating coil may also consist of a layered structure of layers of heating elements and radiator elements. Alternatively, the heat-generating elements protrude at predefined positions adjacent to each other in the volume flow of the liquid medium.

An example of an electric heater designed as an air heater for a motor vehicle is in 5 played. That in a frame 51 held heater contains a layered structure of heating elements (PTC and heating wire) 53, 54 and radiator elements 55 , In the example shown there are three PTC heating elements each 53 and three heating elements 54 shown with a wound in the form of a coil heating wire. The heater is traversed in a direction perpendicular to the image surface of air.

On the left side of the in 5 shown electric heater closes to the heater an outwardly closed housing portion 56 in which an electrical control circuit for the heating elements 53 . 54 is provided. This is done via the contact pins 57 supplied with power, the control circuit depending on the desired heating power, to the heating elements 53 . 54 forwards.

The control circuit adopts the setting of the heating elements 53 . 54 to be provided heating power. For this purpose, it can additionally receive signals via a bus connection, such as a CAN bus (not shown).

Each heating stage (with at least two heating elements 53 . 54 ) of the heater is separately connected to the control circuit. In this case, preferably adjacent heating elements 53 . 54 electrically connected in series with PTC heating elements or a heating conductor wound in the form of a coil. In the example of 5 three heating stages are shown, each with two connected to a heating stage in series heating elements 53 . 54 contain.

For heating stages with more than two heating elements per heating stage, for example, three or four heating elements are correspondingly more in 5 shown heating elements connected in series.

Alternatively to the in 5 shown heating register equipment with an equal number of PTC heating elements 53 and heating element heating elements 54 , for example, two heating elements 54 with heating element and four PTC heating elements 53 be provided. A heating stage is in this case composed of a series connection of a heating element 54 with heating element and two PTC heating elements 53 together.

According to the invention, any number of PTC heating elements 53 with at least one heating element 54 be connected in series with heating conductor for a heating stage. For example, a heating level may be one, two, three, four, five, or even more PTC heating elements 53 and one (two or more) heating element heating elements 54 ,

The heater can have any number of heating stages, each consisting of a series of PTC heating elements 53 and preferably a heating conductor heating element 54 consist. The heating element 54 with the wound into a coil heating wire acts as an inductor for damping the inrush current of the respective heating stage.

To adjust the height of the inductance, in the series connection of a heating stage, if necessary, an additional inductance can be provided which does not serve as a heating element 54 is trained. Such additional inductance in the series connection of the heating elements of a heating stage is preferably on the board of the control circuit in the section 56 of the housing. This inductance thus does not contribute to the heating of the medium in which 5 So example not shown to heat the air flowing through the heater air.

By an additional inductance in the series circuit, which does not contribute to the heating of the medium and is preferably arranged on the circuit board of the control circuit, the Gesamtinduktivität each heating stage in a simple manner, starting from the inductance of the heating element heating element 54 be adjusted. The heating element heating element 54 can thus provide a basic inductance per heating stage. This basic inductance of the heating stage is supplemented in a simple manner by an inductance additionally provided in the series connection. This additional inductance is not coupled to the delivery of heat directly to the medium to be heated and therefore not integrated into the heating coil. Such additional inductance is not related to 5 described heater limited.

The present invention is by no means limited to the in 5 specifically shown and described air heater limited. 5 shows only one possible variant for the design of an air heater with a heater. Other variants are well known in the art.

6 shows a possible embodiment of an electric heater in the form of a water heater in which a liquid medium is heated.

The in 6 shown water heater comprises a housing block 60 which is integrally formed. The housing block 60 is integrally formed with interior housing walls which forms an inlet channel 61 and an outlet channel 62 for the limit liquid medium on the inside. At the channels 61 . 62 opposite side are flat and mutually parallel contact surfaces for arranging a heater 65 educated. The heating coil is composed of a plurality of juxtaposed or layered heat-generating elements and is flowed through by the medium, in this case by the liquid to be heated.

In the housing block 60 may in addition to the area to be heated by the medium to be heated area thereof a completely completed chamber 68 be provided. In addition a dividing wall separates 64 a chamber for the liquid medium to be heated, in this case water, from a control chamber 68 ,

Such a control chamber 68 can be a control circuit with a circuit board 69 take up. On the board, for example, the control transistors for the control of the heating elements are arranged, which adjust the power supplied to the heating elements, for example based on a PWM control.

In addition, on the control board 69 Further inductances (coils) may be provided, which - if necessary - provided in addition to the formed as inductors heating wire heating elements and are each connected in series with the heating elements of a heating stage.

In such an embodiment, although the power loss of the control transistors and the additional inductors contribute to the heating of the medium. As heating elements, however, these additional inductances are not formed and the contribution to the heating of the medium is significantly lower compared to that of the inductors designed as a heating conductor heating element.

Laterally, the in 6 shown housing block 60 preferably sealed by sealing caps (not shown) with corresponding connections.

The present invention is by no means limited to the in 6 specifically shown and described water heater limited. 6 shows only one possible variant for the design of a water heater. Other variants are well known in the art.

The electrical connection of the heating elements of the electric heater is shown schematically in the 7a to 7c shown.

In 7a are examples of the elements of a heating stage 70 played. Every heating level 70 comprises at least one PTC heating element 71 and at least one formed as an inductance heating wire heating element 72 in which a heating conductor is wound in the form of a coil. This series connection of the heating elements 71 . 72 is controlled by a control switch 73 driven. The control switch 73 is preferably a control transistor which is in the form of a power transistor capable of switching high currents.

The electric heater generally includes a plurality of heating stages 70a . 70b . 70c , as in 7b shown. Each of the heating levels 70a . 70b . 70c includes one or more PTC heating elements connected in series 71a . 71b . 71c and at least one further heating element in each case 72a . 72b . 72c , which is formed as an inductance and contains a coil wound in the form of a heating conductor.

The heat output of each of the heating stages is controlled by a separate control switch 73a . 73b . 73c individually adjustable. The heat output of the individual heating stages 70a . 70b . 70c is preferably set with a PWM control. It is advantageous for the burden of the electrical system when the clocking of the individual heating stages takes place with a time lag.

To adapt the inductance of each of the heating stages 70a . 70b . 70c can be an additional inductance 75a . 75b . 75c be provided in each of the heating stages, as in 7c shown. The additional inductance 75a . 75b . 75c is with the heating elements 71 . 72 Each heating stage connected in series.

The heating power provided by the PTC heating elements 71 on the one hand and the inductors designed as heating elements 72 on the other hand is provided in the electric heater is about the same size, that is, on average wear the PTC heating elements 71 and the inductors designed as heating conductors 72 in equal parts to the heating of the medium at.

This distribution of heating powers refers to the steady state condition when the PTC heating element (s) have passed through the point Rmin on the PTC resistance characteristic.

Should the PTC heating elements 71 no longer be able to deliver the full heating power to the medium, for example by a lower air flow, the power distribution shifts again. The resistance of the PTC heating elements and thus the voltage drop across the PTC heating elements 71 increases in relation to the heating element heating element 72 back to. Thus, percentage more power is delivered through the PTC heaters (reducing the overall heater heater power). Preferably, at least 50 percent of the total heating power is provided by the PTC heating elements in the heater.

In an alternative embodiment, the PTC heating elements provide 70 to 90 Percent of the total heating power supplied, the heating element heating elements, which are designed as an inductor, corresponding to only 30 to 10 percent. This division also refers to the settled state of the heating, ie when the initial effects such as high inrush currents have subsided. In operation, the PTC heating elements provide at least 70 percent of the total heating power, in an alternative embodiment even at least 90 percent.

PTC heating elements 71 are equipped with a self-protection against overheating. Since the resistance depends on the temperature, the current flow is automatically reduced as the temperature of the heating element increases. Overheating can thus be effectively prevented.

Heaters with a heat conductor, however, do not have such self-protection. Are heating elements with a heating conductor 72 and PTC heating elements 71 However, according to the invention connected in series, the overheating protection of the PTC heating element 72 also on the series-connected heating element heating elements 71 out.

The protective effect for the heating element heating elements 72 is achieved in the series connection according to the invention characterized in that with increasing temperature an increasing proportion of the voltage at the PTC heating element 71 drops. The proportion of voltage at the heating element heating element 72 decreases, continues to decrease with increasing temperature. Accordingly, the heating power of the heating element heating element also decreases 72 from. When the resistance of the PTC heating element 71 At high temperatures, it has an extremely high resistance, so the total voltage on the PTC heating element drops 71 from and also the series heating wire heating element 71 does not generate heat anymore.

This allows PTC and heating wire heating elements 71 . 72 Combine effectively in a heater by series connection, without affecting the effective overheating protection of the PTC heating elements 72 must be waived.

By series connection of the PTC heating elements with heating element heating elements, which are formed as an inductance by winding the heating element in the form of a coil, the inrush current over a wide voltage range can be kept low. The winding of the heating conductor cuts off the capacitive inrush current of the PTC heating elements.

Further advantages of the embodiment according to the invention are a lower ripple voltage, better EMC (electromagnetic compatibility), the possibility of higher clocking with PMV control (up to 20 kHz), a reduction of the installation space on the control board and a cost savings for the control electronics.

In summary, the present invention relates to an electrical heating device for heating a medium, preferably either water or air. For heating the medium, one or a plurality of heating stages is provided which can be controlled separately. Each of the heating stages is equipped with at least one PTC heating element. In series with the PTC heating element, at least one additional heating element is connected in each heating stage. The further heating element is designed as an inductor and has to a wound in the form of a coil heating conductor. In this way, the inrush current of the PTC heating elements can be lowered and any resulting waste heat emitted to the medium to be heated. The fact that the coil of the inductance is formed of a heating element, it also contributes simultaneously to the heating of the medium. Thus, an efficient heating can be realized with little space.

Claims (14)

Electric heating device for a motor vehicle having at least two electrical heating elements (71, 72) for heating a medium, wherein the two heating elements (71, 72) are electrically connected in series and at least one of the heating elements (72) is a PTC heating element, characterized the further heating element (72) is designed as an inductance and comprises a heating conductor wound in the form of a coil Electric heater after Claim 1 , characterized in that the two electrical heating elements (71, 72) form a first heating stage (70a) and the electric heating device further, separately controllable heating stages (70b, 70c), wherein each of the heating stages (70a, 70b, 70c) a series circuit comprising at least one PTC heating element (71a, 71b, 71c) and a heating conductor wound in the form of a coil as a further heating element (72a, 72b, 72c). Electric heater after Claim 1 or 2 , characterized in that the series connection of a PTC heating element (71) and a coiled in the form of a coil heating element as a further heating element (72) additionally comprises a further series-connected inductance (75), but not as a heating element for the release of heat is formed on the medium. Electric heater after Claim 3 , characterized in that in the series connection of each of the heating stages (70a, 70b, 70c) an additional inductance (75a, 75b, 75c) is provided, which is not designed as a heating element for delivering heat to the medium. Electric heater after Claim 3 or 4 , characterized in that the electrical heating device comprises a control circuit for driving the heating elements (71, 72) and the additional inductance (75), which is not designed as a heating element for emitting heat to the medium, is arranged in the control circuit. Electric heating device according to one of the preceding claims, characterized in that the PTC heating element (71) and formed as a heating element inductance (72) each have the same outer dimensions. Electric heater after Claim 6 characterized in that the heating elements (71, 72) are arranged in the electrical heating device in the form of a heating register, the heating register having a plurality of positions for arranging heating elements, and each of the positions alternatively comprising the arrangement of a PTC heating element (71) or a designed as an inductance heating element (72) allowed. Electric heating device according to one of Claims 2 to 7 , characterized in that the heating power of each heating stage (70a, 70b, 70c) via a PWM control is adjustable and the PWM control of the individual heating stages (70a, 70b, 70c) takes place with a time offset of the PWM clocking between the heating stages. Electric heating device according to one of the preceding claims, characterized in that the total heating power of the electric heating device is provided in equal parts by the PTC heating elements (71) and the heating elements (72) designed as an inductance. Electric heating device according to one of Claims 1 to 8th , characterized in that the total heating power of the electric heater is at least 70 percent provided by the PTC heating elements (71). Electric heating device according to one of the preceding claims, characterized in that the electrical heating device is designed for an operating voltage in automotive high voltage range. Electric heating device according to one of the preceding claims, characterized in that the electrical heating device for heating a liquid is designed as a medium to be heated. Electric heating device according to one of Claims 1 to 11 , characterized in that the electrical heating device is designed for heating air as medium to be heated. Motor vehicle with an electric heater according to one of the preceding claims.

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