CN109693514B

CN109693514B - Electric heater for motor vehicle

Info

Publication number: CN109693514B
Application number: CN201811233223.7A
Authority: CN
Inventors: 托马斯·格施温德
Original assignee: Eberspaecher Catem GmbH and Co KG
Current assignee: Eberspaecher Catem GmbH and Co KG
Priority date: 2017-10-23
Filing date: 2018-10-22
Publication date: 2022-04-15
Anticipated expiration: 2038-10-22
Also published as: CN109693514A; DE102017218899A1

Abstract

The present invention relates to an electric heater for heating a medium, preferably water or air. For heating the medium, one or more individually controllable heating stages are provided. Each heating stage is equipped with at least one PTC heating element. In each heating stage, at least one additional heating element is connected in series with the PTC heating element. The additional heating element is designed as an inductor and for this purpose comprises a heating conductor wound in the form of a coil. In this way, the inrush current of the PTC heating element can be reduced and the generated residual heat can be released into the medium to be heated. Since the coil of the inductor is constituted by a heating conductor, it also contributes to heating the medium. In this way, efficient heating can be achieved in a very small installation space.

Description

Electric heater for motor vehicle

Technical Field

The invention relates to an electric heater for a motor vehicle, comprising a plurality of heating elements, in particular PTC heating elements.

Background

Electric heaters are used in motor vehicles, for example, as auxiliary heaters to supplement the heating of the passenger compartment and other components, which is achieved primarily by the waste heat of the engine, or to allow heating of the vehicle, for example, when the vehicle is stationary.

Electric heaters are particularly important for vehicles with electric or hybrid drive, in the case of motor vehicle drive units which do not discharge or do not have sufficient waste heat to heat or condition the vehicle with an air conditioner. This is advantageous when a heater for an electric or hybrid vehicle is adapted to provide heat required by or at least supporting processes occurring in various system components of the motor vehicle (for example, preheating of the vehicle battery) in addition to the heat required for heating the passenger compartment of the motor vehicle.

Heaters for use in electric or hybrid vehicles are supplied with operating voltages in the high voltage range of the automobile (above 60 volts, preferably several hundred volts, up to 500 volts, typically between 280 volts and 430 volts (e.g. 300 volts or 380 volts) because the vehicle battery used supplies such on-board system voltages, the heating capacity of such high voltage heaters is of the order of 3 to 6kW (kilowatts) compared to the order of 1 to 1.7kW (e.g. 1.2kW) in the case of 12 volt auxiliary heaters for motor vehicles.

In electric heaters installed in motor vehicles, resistive heating elements, in particular PTC (positive temperature coefficient) heating elements, are used. PTC heating elements are self-regulating in that they exhibit a higher resistance with increasing heat and therefore allow a smaller amount of current to pass at the same voltage. The PTC element will therefore heat up to a defined maximum temperature. The self-regulating nature of the PTC heating element thereby prevents overheating. The surface temperature of the PTC element must not exceed a certain maximum surface temperature during operation with a specific operating voltage. This maximum surface temperature is a characteristic of the PTC heating element. The heat generated by the PTC element is released into a fluid medium, in particular a stream of air or water.

Fig. 1 shows a typical resistance curve of a PTC element as a function of temperature.

After the energization and the subsequent heating, the PTC element will reach a point on the PTC characteristic curve 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 higher than during normal operation.

PTC heating elements in the form of thin ceramic plates also have capacitive inrush currents due to their flat structural design.

Thus, PTC heating elements exhibit high inrush currents, which makes such heaters more expensive to manufacture and more difficult to operate in a vehicle electrical system.

Disclosure of Invention

It is an object of the present invention to provide an electric heater which avoids such inrush currents and allows efficient heating.

This is achieved by the features of claim 1.

The electric heater for a motor vehicle according to the invention comprises at least two electric 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 other heating element is a heating conductor wound in the form of a coil serving as an inductance.

A particular approach of the present invention is to connect an inductor in series with the PTC heating element, the inductor reducing inrush current while acting as a heating element. For this purpose, the inductance is configured such that the heating wire is wound in the form of a coil. Thus, the component acts as both a heater and an inductor. Thus, it can release heat generated by the heating wire into the medium. At the same time, the heat generated by the inductance can also be used to heat the medium.

By the solution according to the invention, the inrush current can be kept low and the peak of the capacitive inrush current can be limited. Due to the dual use of the additional heating element as both an inductance and a heating element, the space required for the heater can be kept small, since it is not necessary to provide an inductance separately.

Preferably, the heater comprises a plurality of individually controllable heating stages connected in parallel, each heating stage comprising a series connection of at least one PTC heating element and an inductance of a heating conductor wound in the form of a coil.

In this way, the flexible adjustability of the heating power and the possibility of additionally connecting the heating stages of the known multi-stage electric heater are maintained, and the advantages according to the invention are achieved for each heating stage. Each heating stage comprises a combination of at least one PTC heating element and an inductance constituted by a heating conductor. It is thus possible to reduce the inrush current for each heating stage and additionally to supply the heat of the inductance to the medium together with the heat of the heating conductor.

Preferably, the series connection comprising the PTC heating element and the heating conductor wound in the form of a coil is additionally supplemented by an inductance of the series connection, so that each heating stage has such an additional inductance. However, the additional inductance is not configured to release heat to the medium.

In this way, the inductance of the heating stage can be variably adjusted. To this end, an additional inductance is added to each series connection of heating elements (i.e. for each heating stage). However, this additional inductance cannot be configured as a heating element, i.e. it is not a coil wound by a heating conductor. Thus, each heating stage comprises at least two inductors. However, only a portion of the inductance connected in series with the PTC heating element contributes to the heating medium, i.e. constitutes the inductance of the heating element. Thus, the induction characteristics of the heating stage can be easily adjusted, for example, if the inductivity of the inductance of the heating element is configured to be insufficient.

Preferably, further inductances are also provided in the heater (i.e. in a control circuit arranged in the housing of the heater) which do not contribute to the heating medium.

This makes it easy to integrate the additional inductance of each heating stage into the known structural design of the heater.

Preferably, the PTC heating element and the heating element configured as an inductor have the same outer dimensions. In this way, the electric heater can be equipped with a PTC heating element and a heating element configured as an inductor as desired.

In addition, preferably, the heating element is arranged in the form of a heating register in the electric heater. The heating register comprises a plurality of positions for arranging the heating elements. Each position optionally allows the arrangement of a PTC heating element or a heating element configured as an inductance.

Using a heating element and a mounting location which are not dependent on the type of heating element (i.e. PTC or inductance), a heater suitable for various requirements can be manufactured particularly easily. The heating register may be constituted by a layered structure of heating elements (optionally also comprising heat sink elements). According to another alternative, a predetermined position is provided in the housing, where the heating element (PTC or heater wire) can be mounted.

Preferably, the heating stage is PWM (pulse width modulation) controlled. The heating power can thus be easily adjusted continuously.

The total heating power of the heating stage or of the electric heater is preferably produced in equal proportions by the PTC heating element and the inductance configured as a heating element. This applies in particular when the heating elements, in particular PTC heating elements, are operated in the steady state, i.e. when they are subjected to a particular energization behavior (in particular the point Rmin on the resistance characteristic curve of the PTC heating elements). The total heating power includes the heating power of the PTC heating element and the heating power configured as the inductance of the heating element.

Preferably, at least 70% of the total heating power of the electric heater is generated by the PTC heating element in a steady state of the heating operation.

The electric heater may be configured as an air heater (air as the medium to be heated), or as a water heater (liquid such as water as the medium to be heated).

The heater according to the invention can also be used for other tasks of a motor vehicle to provide the necessary process heat, to preheat or to maintain the temperature of components essential to operation, such as a battery.

The invention comprises in particular a motor vehicle, preferably an electric or hybrid vehicle, with an electric heater constructed as described above, preferably with an operating voltage in the high-voltage range of the vehicle.

Further advantageous embodiments are the subject of the dependent claims.

Drawings

The invention will be explained below on the basis of preferred embodiments with reference to the attached drawings, in which:

fig. 1 shows a typical resistance curve of a PTC heating element as a function of temperature;

fig. 2 shows a perspective side view of an exemplary heat-generating PTC heating element in an exploded view;

fig. 3a to 3d show perspective views of the internal structure of an exemplary inductor also as a heating element;

fig. 4 shows a detail of a schematic cross-section of a layered structure of a heating register through an air heater.

FIG. 5 shows a top view of an exemplary air heater with a heating register;

FIG. 6 shows a perspective side view of an exemplary water heater with a heating register; and

fig. 7a to 7c show schematic diagrams of exemplary series connections of electric heaters with one or more heating stages.

Detailed Description

According to the invention, for each heating stage, the electric heater uses a series connection with two different types of heating elements, namely a PTC heating element on the one hand and a (resistive) heating conductor on the other hand, which also functions as an inductance. The two types of heating elements are preferably prefabricated as heating elements having predetermined dimensions so that they can be used in any way, i.e. interchanged, to construct an electric heater.

The electric heater includes a plurality of heat generating elements of the same size, which include PTC elements or heating wires. In this way, the individual components of the electric heater consisting of the PTC heating element and the heating element with heating wire can be constructed in any manner. The heating elements are connected in series (electrically) in the electric heater, so that a heating stage comprises at least one PTC heating element and one heating element with a heating filament (which is designed as an inductance).

The electric heater preferably comprises not only a single heating stage, but a plurality of individually controllable heating stages. Each heating stage may be individually energised in accordance with the required heating power. Additionally or alternatively, the heating power of each heating stage is set by PWM (pulse width modulation). The heating stages can be controlled with a time offset to keep the load on the vehicle electrical system low.

Fig. 2 shows an exemplary embodiment of a heat-generating element having a PTC element. The heating elements comprise respective flat tubes 28, inside which sleeve-shaped (i.e. cylindrical) insulators 28.1 in the form of insulating films, for example polyimide or Kapton, are aligned. Contact plates 28.2, 28.3 are accommodated in the insulating body 28.1, receive the PTC element 28.4 between them and are in direct contact with the PTC element 28.4 in an electrically conductive manner. The insulator 28.1 may comprise an electrically insulating heat resistant film which may be coated with PTFE on one or both sides thereof. The insulating film may be welded into the flat tubes 28 under pressure and heat, for example, when the heater is in operation. The PTC element 28.4 is provided with a metallization, which is applied as a coating to the PTC element 28.4.

Each contact plate 28.2 and 28.3 has integrally formed thereon a contact tongue 28.5 by stamping and bending. On one side, the flat tube 28 is closed by plastic end plugs 28.6, which plastic end plugs 28.6 are respectively glued in a sealing manner in the flat tube 28 and in the insulator 28.1. On the opposite side, an end cap 28.7 is provided in a similar manner, said end cap 28.7 having a guide sleeve 28.8 integrally formed thereon, which guide sleeve 28.8 is made of plastic and serves for a corresponding contact tongue 28.5. It can be seen that the contact tongues 28.5 are bent at the end sides and are located approximately at a height corresponding to the middle of the height of the PCT element 28.4.

An insulating layer such as a ceramic plate, a plastic foil, or a plastic foil-coated ceramic plate may also be used as an insulator to the main side surfaces of the flat tubes 28. The insulator is an electrical insulator which should preferably have a good thermal conductivity of at least 20W/(m · K). The layers of the layered structure formed by the insulating body 28.1, the contact plates 28.2, 28.3 and the PTC element 28.4 are usually inserted loosely into the flat tube 28. These elements are first axially fixed in the flat tubes 28 by end caps 28.7 and end plugs 28.6, respectively.

The present invention is not limited to the embodiment of the PTC heating element specifically illustrated in fig. 2 and described herein. Fig. 2 shows only one possible variant of the design of the PTC heating element for installation in a heating register. Other variations are generally known from the prior art.

Fig. 3a to 3d show exemplary structural designs of a heating element with a heating wire configured as an inductance. The heat-generating element comprises flat tubes 30 shown in fig. 3d, the outer dimensions of which correspond to the outer dimensions of the flat tubes 28 of the PTC heating element shown in fig. 2 and which can be used interchangeably with said flat tubes 28. The flat tubes 30 receive therein a carrier 31 made of an insulating material. Suitable support materials are materials having particularly good insulating properties and good heat resistance, for example synthetic mica (synthetic mica). Fig. 3a shows a possible shape of the carrier 31.

The heating conductor 32 is wound on the carrier 31 as shown in fig. 3 b. The material that can be used for the heating conductor 32 is a heating conductor alloy that has high temperature resistance, preferably with a substantially constant specific resistance over a wide temperature range (e.g., constantan).

The length of the heating conductor 32 depends on the desired inductance characteristics and the heating power to be generated. Here, the heating conductor 32 is wound in the form of a spiral or double helix, if desired in layers, on the carrier 31.

In the embodiment shown in fig. 3, contact tongues 33 are shown at one end of the carrier in the longitudinal direction, through which contact tongues the heating conductor 32 is electrically contacted. The contact tongues 33 are preferably also configured to correspond to the contact tongues of the PTC heating element according to fig. 2, so that the two heating elements can be used interchangeably in an electric heater. For this purpose, as in fig. 2, for example, the ends of the flat tubes 28 can be closed by end plugs 28.6 and end caps 28.7, respectively, the end caps 28.7 being provided with guide sleeves 28.8 for electrical contacting.

In fig. 3c, the outer insulation 35 of the carrier 31 with the wound heating conductor 32 is shown. The insulator 35 should be particularly heat resistant and should have good thermal conductivity. In this case, a suitable material is, for example, synthetic mica (synthetic mica).

The carrier 31 with the wound heating conductor 32 and the insulator 35 is inserted into a flat tube 30, which flat tube 30 corresponds to the flat tube 28 described in connection with the PTC heating element in fig. 2. The coils made of the heating wire 32 may be axially fixed in the flat tube 28 using suitable end caps and end plugs of the type described in connection with fig. 2.

The present invention is in no way limited to the embodiment specifically illustrated in fig. 3 and described herein. Fig. 3 shows only one possible variant of the structural design of the heating element as an inductance, in which case a heating conductor in the form of a coil is used for heating and generating heat.

A heating element comprising a PTC element or a heating wire is arranged in the electric heater, preferably in the form of a heating register. Fig. 4 shows one schematic example of a heating register structure for an air heater. The heating register 40 consists of a layered structure of

heating elements

41, 42 and a radiator element 43. In addition, further layers may be provided, for example contact plates, electrically insulating layers, etc. Air flows through the layered structure in a direction perpendicular to the image area.

In the structure shown in fig. 4, the

heating elements

41, 42 are arranged between the radiator elements 43. In the layer comprising the

heating elements

41, 42, a PTC heating element 41 or a heating conductor heating element 42 is provided. Preferably, each type of heat generating element (i.e. PTC or heating conductor with inductive properties) alternates with the heat sink element in successive layers to release heat to the medium flowing therethrough.

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

As mentioned above, the dimensions and contacts of the

heating elements

41, 42 are preferably identically constructed, so that these heating elements can be used in any manner in the register 40.

The illustration of fig. 4 shows the details of the heating register only in a schematic way. In addition, further layers comprising

heating elements

41, 42 and heat sink elements may be provided, which layers correspond, for example, to additional heating stages.

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

Fig. 5 shows one example of an electric heater configured as an air heater for a motor vehicle. The heating register held in the frame 51 comprises a layered structure of heating elements (PTC and heating wires) 53, 54 and a radiator element 55. In the example shown, three PTC heating elements 53 and three heating elements 54 with heating wires wound in the form of coils are shown, respectively. The air flows through the heating recorder in a direction perpendicular to the image area.

On the left side of the electric heater shown in fig. 5, the heating register is followed by an externally closed housing section 56, in which an electrical control circuit for the

heating elements

53, 54 is arranged. The control circuit is supplied with electrical energy via contact pins 57, which the control circuit delivers to the

heating elements

53, 54 according to the required heating power.

The control circuit sets the heating power to be generated by means of the

heating elements

53, 54. To this end it may also receive additional signals via a bus connection, such as a CAN bus (not shown).

Each heating stage of the heater (comprising at least two heating elements 53, 54) is connected to a control circuit, respectively. Preferably,

adjacent heating elements

53, 54 comprising PTC heating elements or heating conductors wound in the form of coils are electrically connected in series. In the example according to fig. 5, three heating stages are shown, each heating stage comprising two

heating elements

53, 54, which

heating elements

53, 54 are connected in series to constitute one heating stage.

In the case of heating stages comprising more than two heating elements per heating stage, for example three or four heating elements, a suitably larger number of the heating elements shown in fig. 5 are connected in series.

Instead of the heating register shown in fig. 5, which is equipped with the same number of PTC heating elements 53 and heating conductor heating elements 54, it is possible to provide, for example, two heating elements 54 with heating conductors and four PTC heating elements 53. In this case, a heating stage is formed by a series connection of a heating element 54 with a heating conductor and two PTC heating elements 53.

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

The heater may have any number of heating stages, each heating stage comprising a series connection of a PTC heating element 53 and preferably one heating conductor heating element 54. The heating element 54, which comprises a coil-wound heating wire, functions as an inductance for suppressing the inrush current of the respective heating stage.

In order to adjust the magnitude of the inductance ratio, additional inductances which are not designed as heating elements 54 can also be provided in the series connection of the heating stages, if required. Such an additional inductance is preferably arranged on the circuit board of the control circuit in the section 56 of the housing in the series connection of the heating elements of the heating stage. The inductance thus does not contribute to the heating of the medium, i.e. in the example shown in fig. 5 it does not contribute to the heating of the air flowing through the heating register.

By means of the additional inductance in the series circuit, which does not contribute to the heating of the medium and which is preferably arranged on the circuit board of the control circuit, the total inductance of each heating stage can easily be adjusted starting from the inductance of the heating element 54. The heating conductor heating element 54 may thus provide a substantial inductance for each heating stage. This basic inductance of the heating stage is simply supplemented by an additional inductance provided in the series connection. The additional inductance is not directly coupled to the medium to be heated in order to release heat into it and is therefore not integrated in the heating register. Such additional inductance is not limited to the heater described in connection with fig. 5.

The present invention is in no way limited to the air heater specifically shown and described in fig. 5. Fig. 5 shows only one possible variant for constructing an air heater with a heating register. Other variations are generally known from the prior art.

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

The water heater shown in fig. 6 includes an integrally formed housing block 60. The housing block 60 is integrally formed with the housing interior walls defining an inlet channel 61 and an outlet channel 62 for the liquid medium therein. On the side opposite to the

channels

61, 62, flat contact surfaces are formed extending parallel to each other to arrange a heating register 65 thereon. The heating register is constituted by a plurality of juxtaposed or layered heating elements through which the medium, i.e. in this case the liquid to be heated, flows.

In addition to the region through which the medium to be heated flows, the housing block 60 also has a chamber 68 arranged therein, which chamber 68 is completely closed off from said region. To this end, the partition 64 separates a chamber of the liquid medium to be heated (in the present case water) from the control chamber 68.

Such a control chamber 68 may house control circuitry having a circuit board 69. Arranged on the circuit board are, for example, control transistors for controlling the heating elements and regulating the current supplied to the heating elements, for example on the basis of PWM control.

In addition, the control board 69 may be provided thereon with other inductances (coils) which are provided in addition to the heating elements of the heating wire constructed as inductors, if necessary, and which are each connected in series with the heating elements of the heating stages.

With this structural design, the power dissipation of the control transistor and the additional inductance may indeed contribute to the heating of the medium. However, these additional inductances are not configured as heating elements and contribute significantly less to the heating medium than do the inductances configured as heating conductor heating elements.

On the side, the housing block 60 shown in fig. 6 is preferably sealed by a sealing cover (not shown) provided with suitable connections.

The present invention is in no way limited to the water heater specifically shown and described in fig. 6. Fig. 6 shows only one possible variant of the structural design of the water heater. Other variations are generally known from the prior art.

The electrical wiring of the heating element of the electric heater is schematically shown in fig. 7a to 7 c.

In fig. 7a, the elements of the heating stage 70 are schematically shown. Each heating stage 70 comprises at least one PTC heating element 71 and at least one heating wire heating element 72, which is designed as an inductor, in which case the 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. The control switch 73 is preferably a control transistor in the form of a power transistor, which is capable of switching on and off high currents.

The electric heater typically comprises a plurality of

heating stages

70a, 70b, 70c, as shown in fig. 7 b. Each

heating stage

70a, 70b, 70c comprises one or more

PTC heating elements

71a, 71b, 71c and at least one

further heating element

72a, 72b, 72c connected in series, which

heating elements

72a, 72b, 72c are constructed as inductors and comprise a heating conductor wound in the form of a coil.

The heating power of each heating stage can be adjusted individually by

separate control switches

73a, 73b, 73 c. The heating power of the

individual heating stages

70a, 70b, 70c is preferably regulated by means of PWM control. Here, it is advantageous for the load on the vehicle electrical system when the timing of the heating stages occurs with a time offset.

In order to adjust the inductivity of each

heating stage

70a, 70b, 70c, an

additional inductance

75a, 75b, 75c may be provided in each heating stage, as shown in fig. 7 c. An

additional inductance

75a, 75b, 75c is connected in series with the

heating element

71, 72 of each heating stage.

In an electric heater, the heating power generated by the PTC heating element 71 on the one hand and the inductance 72 configured as a heating element on the other hand is substantially the same, i.e. on average the PTC heating element 71 and the inductance 72 configured as a heating conductor contribute equally to the heating medium.

This distribution of the heating power when the PTC heating element has passed the point Rmin on the PTC resistance characteristic curve is referred to as the steady state.

If the PTC heating element 71 will no longer be able to discharge the full heating power to the medium, for example, the power distribution will change again due to the lower air flow rate. The resistance of the PTC heating element and thus the voltage drop over the PTC heating element 71 increases again with respect to the heating conductor heating element 72. As a result, the PTC heating elements provide more power on a percentage basis (while the total heating power of the heater is reduced). Preferably, at least 50% of the total heating power of the heater is generated by the PTC heating element.

According to an alternative embodiment, the PTC heating element provides 70 to 90% of the total heating power generated, whereas the heating conductor heating element configured as an inductance provides only 30 to 10%. This profile is also referred to as the steady state of heating, i.e., when the initial effects such as high inrush current are reduced. In operation, according to an alternative embodiment, the PTC heating element provides at least 70%, even at least 90%, of the total heating power.

The PTC heating element 71 is provided with self-protection against overheating. Since the resistance depends on the temperature, the current will automatically decrease if the temperature of the heating element increases. Overheating can be effectively prevented.

However, heaters with heating conductors do not have such self-protection. However, if the heating element comprising the heating conductor 72 and the PTC heating element 71 are connected in series according to the invention, the overheating protection of the PTC heating element 71 will also have an effect on the heating conductor heating element 72 which is connected in series.

In the series connection according to the invention, the protective effect on the heating conductor heating element 72 is achieved by the fact that: as the temperature increases, an increasing percentage of the voltage will fall on the PTC heating element 71. As the temperature increases, the percentage of voltage falling on the heating conductor heating element 72 will become lower. The heating power of the heating element 72 is correspondingly reduced. When the resistance of the PTC heating elements 71 has an extremely high resistance value at high temperatures, the total voltage will fall on the PTC heating elements 71 and the series-connected heater wire heating elements 72 will also no longer generate any heat.

Thus, the PTC and

wire heating elements

71, 72 can be effectively combined by series connection in the heater, without having to do so without the PTC heating element 71 having effective over-temperature protection.

By connecting the PTC heating element in series with a heating conductor heating element which is constructed as an inductance by winding the heating conductor in the form of a coil, the inrush current can be kept low over a wide voltage range. The capacitive inrush current of the PTC heating elements is limited by the winding of the heating conductor.

Other advantages of embodiments according to the invention are lower ripple voltage, better EMC (electromagnetic compatibility), possibility of using higher clocks of PMV control (up to 20kHz), reduction of installation space on the control board and cost saving of control electronics.

In summary, the present invention relates to an electric heater for heating a medium, preferably water or air. For heating the medium, one or more heating stages are provided, which can be controlled individually. Each heating stage is equipped with at least one PTC heating element. In each heating stage, at least one additional heating element is connected in series with the PTC heating element. The additional heating element is designed as an inductor, which for this purpose comprises a heating conductor wound in the form of a coil. In this way, the inrush current of the PTC heating element can be reduced, and the generated residual heat can be released into the medium to be heated. Since the coil of the inductor is constituted by a heating conductor, the inductor also contributes to heating the medium. In this way, efficient heating can be achieved in a very small installation space.

Claims

1. An electric heater for a motor vehicle, comprising at least two heating elements (71, 72) for heating a medium, the two heating elements (71, 72) being electrically connected in series, and at least one of the heating elements (71) being a PTC heating element,

it is characterized in that

The other heating element (72) is configured as an inductor and comprises a heating conductor wound in the form of a coil, the winding of the heating conductor limiting the capacitive inrush current of the PTC heating element.

2. An electric heater according to claim 1, characterised in that the two heating elements (71, 72) form a first heating stage (70 a) and in that the electric heater comprises additional individually controllable heating stages (70 b, 70 c), wherein each heating stage (70 a, 70b, 70 c) comprises a series connection of at least one PTC heating element (71 a, 71b, 71 c) and a heating conductor as an additional heating element (72 a, 72b, 72 c), which is wound in the form of a coil.

3. An electric heater according to claim 2, characterised in that the series connection of the PTC heating element (71) and the heating conductor wound in the form of a coil as the further heating element (72) further comprises an additional inductance (75), which additional inductance (75) is connected in series but is not configured as a heating element emitting heat to the medium.

4. An electric heater according to claim 3, characterized in that an additional inductance (75 a, 75b, 75 c) is provided in the series connection of each heating stage (70 a, 70b, 70 c), which additional inductance (75 a, 75b, 75 c) is not configured as a heating element for emitting heat to the medium.

5. An electric heater according to claim 3, characterised in that the electric heater comprises a control circuit for controlling the heating elements (71, 72), and in that the additional inductance (75) of a heating element which is not configured for emitting heat to the medium is arranged in the control circuit.

6. Electric heater according to claim 1 or 2, characterized in that the PTC heating element (71) and the inductance configured as heating element (72) both have the same outer dimensions.

7. The electric heater according to claim 6, characterized in that the heating elements (71, 72) are arranged in the electric heater in the form of a heating register comprising a plurality of positions for arranging heating elements, and each of said positions allows alternately arranging PTC heating elements (71) or heating elements (72) configured as inductances.

8. Electric heater according to claim 2, characterized in that the heating power of each heating stage (70 a, 70b, 70 c) can be adjusted by PWM control, and in that the PWM control of the heating stages (70 a, 70b, 70 c) is performed with PWM clock offsets between the heating stages.

9. The electric heater according to claim 1 or 2, characterized in that the total heating power of the electric heater is generated equally by the PTC heating element (71) and the heating element (72) configured as an inductance.

10. An electric heater according to claim 1 or 2, characterized in that at least 70% of the total heating power of the electric heater is generated by the PTC heating element (71).

11. An electric heater as claimed in claim 1 or 2, configured for operating voltages in the high voltage range of a motor vehicle.

12. An electric heater as claimed in claim 1 or 2, configured for heating a liquid as a medium to be heated.

13. An electric heater as claimed in claim 1 or 2, configured for heating air as the medium to be heated.

14. A motor vehicle comprising an electric heater according to any preceding claim.