ELECTRICAL HEATER WITH HEATING REGISTERS MADE OF PTC-ELEMENTS WHICH ARE COUPLED THERMALLY IN SERIES

Abstract

A heating arrangement may include a first PTC heating device with at least one first PTC heating element, and a second PTC heating device with at least one second PTC heating element. The first and second PTC heating devices may be arranged in a through-flow direction one behind the other. The first and second PTC heating devices may be controllable independently of one another via a controller.

Claims

1. A heating arrangement, comprising: a first PTC heating device with at least one first PTC heating element; and a second PTC heating device with at least one second PTC heating element; wherein the first and second PTC heating devices are arranged in a through-flow direction one behind the other; and wherein the first and second PTC heating devices are controllable independently of one another via a controller.

2. The heating arrangement according to claim 1, wherein the first PTC heating device has a first reference temperature T.sub.1Ref and the second PTC heating device a second reference temperature T.sub.2Ref, wherein (T.sub.2Ref−T.sub.1Ref)>5° C. applies.

3. The heating arrangement according to claim 2, wherein one of:
(T.sub.2Ref−T.sub.1Ref)>10° C.; or
(T.sub.2Ref−T.sub.1Ref)>15° C.

4. The heating arrangement according to claim 1, wherein the controller controls at least the second PTC heating device via pulse width modulation.

5. The heating arrangement according to claim 2, wherein T.sub.1Ref<155° C.

6. The heating arrangement according to claim 2, wherein T.sub.2Ref>165° C.

7. The heating arrangement according to claim 1, wherein the second PTC heating device is arranged in the through-flow direction after the first PTC heating device.

8. The heating arrangement according to claim 1, wherein at least one further PTC heating device is arranged in the through-flow direction after the second PTC heating device, wherein the at least one further PTC heating device includes at least one further PTC heating element and a reference temperature T.sub.wRef, and wherein (T.sub.wRef−T.sub.2Ref)>5° C.

9. The heating arrangement according to claim 1, wherein at least the second PTC heating device has at least one of a size and a form other than the first PTC heating device.

10. The heating arrangement according to claim 1, wherein at least the first and the second PTC heating devices are permanently joined to one another.

11. A method for operating a heating arrangement comprising adjusting a heating output of at least one of a first PTC heating device and a second PTC heating device via pulse width modulation, wherein the first and second PTC heating devices each has a respective at least one PTC heating element, are arranged in a flow-through direction one behind the other, and are controllable independently of one another via a controller.

12. The method according to claim 11, wherein the first PTC heating device is operated without pulse width modulation and the second PTC heating device with pulse width modulation.

13. The method according to claim 12, wherein: a first range exclusively, the second PTC heating device is controlled with a pulse width of 0%≤w≤100% such that a heating output within the first range is adjusted; at the end of the first range, the pulse width w is adjusted to 0% and the second PTC heating device is switched off, and the first PTC heating device is operated with constant voltage without pulse width modulation; and in a second range, the first PTC heating device is continued to be operated with constant voltage and the second PTC heating device is subjected to a pulse width of 0%≤w≤100% and such that heating output is adjusted.

14. An air-conditioning system of a motor vehicle comprising a heating arrangement including: a first PTC heating device with at least one first PTC heating element; and a second PTC heating device with at least one second PTC heating element; wherein the first and second PTC heating devices are arranged in a through-flow direction one behind the other; and wherein the first and second PTC heating devices are controllable independently of one another via a controller.

15. The air conditioning system according to claim 14 wherein the first PTC heating device has a first reference temperature T.sub.1Ref and the second PTC heating device a second reference temperature T.sub.2Ref, wherein (T.sub.2Ref−T.sub.1Ref)>5° C.

16. The air conditioning system according to claim 15, wherein one of:
(T.sub.2Ref−T.sub.1Ref)>10° C.; or
(T.sub.2Ref−T.sub.1Ref)>15° C.

17. The air conditioning system according to claim 14, wherein the controller controls at least the second PTC heating device via pulse width modulation.

18. The air conditioning system according to claim 15, wherein T.sub.1Ref<155° C.

19. The air conditioning system according to claim 15, wherein T.sub.2Ref>165° C.

20. The air conditioning system according to claim 14, wherein the second PTC heating device is arranged in the through-flow direction after the first PTC heating device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] It shows, in each case schematically:

[0023] FIG. 1 shows a heating arrangement according to the invention,

[0024] FIG. 2 shows a resistance-temperature profile of a possible PTC heating element,

[0025] FIG. 3 shows a heating output of a pulse width-modulated second PTC heating device,

[0026] FIG. 4 shows a heating output of a first PTC heating device that is not pulse width-modulated,

[0027] FIG. 5 shows a cumulated heating output of the first PTC heating device and the second PTC heating device.

DETAILED DESCRIPTION

[0028] According to FIG. 1, a heating arrangement 1 according to the invention, which can be arranged for example in an air-conditioning system 2 of a motor vehicle 3, comprises a first PTC heating device 4 having at least one, here altogether three first PTC heating elements 5, and a second PTC heating device 6 having at least one, here likewise altogether three second PTC heating elements 7. Here, the two PTC heating devices 4, 6 are arranged one after the other in the through-flow direction 8 and are therefore flowed through one after the other by a fluid flow to be heated, for example air 10. Likewise provided is a device 9, for example a control/regulating device, via which the two PTC heating devices 4, 6 can be controlled independently of one another. This offers the major advantage that depending on the requested heating output H either the first or the second PTC heating device 4, 6 or both PTC heating devices 4, 6 can be activated.

[0029] Through the alternative controlling of both PTC heating devices 4, 6 or their cumulative controlling with different outputs each it is possible for the first time to completely cover an entire requested output curve with respect to a heating output H and not only, as in the past, individual working points or extracts of the heating output range, as has been possible with conventional electric heaters that could only be switched on and switched off.

[0030] In an advantageous further development of the heating arrangement 1 according to the invention, the first PTC heating device 4 has a first reference temperature T.sub.1Ref and the second PTC heating device 6 a second reference temperature T.sub.2Ref, wherein (T.sub.2Ref−T.sub.1Ref)>5° Celsius or >5 Kelvin applies.

[0031] Here, the reference temperature T.sub.Ref is determined as follows: according to FIG. 2, an exemplary resistance-temperature curve of a possible PTC heating device 4, 6 is shown. Up to a starting temperature T.sub.A, such a PTC heating device 4, 6 has an NTC range (negative temperature coefficient), in which the resistance R falls with increasing temperature T until the resistance R, at the starting temperature T.sub.A, has reached its low point. The temperature at the turning point is also referred to as T.sub.A. Following this, the PTC heating device 4, 6 upon a further heating changes into the PTC range (positive temperature coefficient), in which the resistance R increases greatly with the temperature T. The reference temperature T.sub.Ref is not determined in each PTC heating device 4, 6 in that at the starting temperature T.sub.A twice the resistance according to FIG. 2, i.e. in the example R=20 Ohm, is assumed and at this ohmic value a point of intersection with the resistance-temperature curve searched in the PTC range. At this point, the associated reference temperature T.sub.Ref is read off the abscissa. Through the arrangement of two PTC heating devices 4, 6 that are different with respect to their reference temperature T.sub.Ref it is possible to operate the two PTC heating devices 4, 6 nearer to their optimal working point and because of this improve both the output of the heating arrangement 1 and also minimise any voltage or current peaks that may occur.

[0032] Since upon an activation of the heating arrangement 1 the air 10 flowing through is already heated in the first PTC heating device 4 it is favourable to form the second PTC heating device 6 with a significantly higher reference temperature T.sub.2Ref in order to adapt the optimal heating output range of the second PTC heating device 6 to the temperature level of the air 10 already increased by the first PTC heating device 4. Here, (T.sub.2Ref−T.sub.1Ref)>10° Celsius or >15° Celsius particularly preferably applies for example, wherein for example the reference temperature T.sub.1Ref of the first PTC heating device 4 can be smaller than or equal to 155° Celsius while the reference temperature T.sub.2Ref of the second PTC heating device 6 can be greater than or equal to 165° Celsius. By way of this, the circumstance that the air 10 or generally the fluid flowing through the heating arrangement 1 when flowing through the second PTC heating device 6 already has a higher temperature level is taken into account.

[0033] In a further advantageous embodiment of the solution according to the invention the device 9 is designed in such a manner that it can control at least the second PTC heating device 6 by means of pulse width modulation. Such a pulse width modulation is shown in FIG. 3 in different diagrams, wherein on the abscissa the heating output in percent and on the ordinate the pulse width w likewise in percent is plotted.

[0034] In the diagrams of FIGS. 3 to 5, the heating outputs H of two PTC heating devices 4, 6 are recorded, which produce the same heating output. With in each case fully activated PTC heating device 4, 6 these bring 100% of their output each, which in each case corresponds to 50% of the heating output of the heating arrangement 1.

[0035] Looking at FIG. 3 a pulse width-modulated second PTC heating device 6 is noticeable in these diagrams, in which the pulse width-dependent heating output H in the first and second range 11, 12 in the points A and B at 0% modulated pulse width w amounts to 0%, while the heating output H in the points C and D with 100% pulse width w there amounts to 100% of the heating output H of the second PTC device 6. This corresponds to 50% of the heating output of the entire heating arrangement 1.

[0036] In the diagram of FIG. 4 the first PTC heating device 4 is shown, in which no pulse width modulation whatsoever is carried out, so that the same can be merely switched on and off and then generates either 0 or 100% heating output of the first PTC heating device 4. Here, the first PTC heating device 4 is shown in the range 11 in the switched-off state and in the second range 12 in the switched-on state. Here, it produces in the switched-on state 100% of the heating output H of the first PTC heating device 4, i.e. H.sub.1, which corresponds to 50% of the heating output H.sub.2 of the entire heating arrangement 1 with simultaneously activated first and second PTC heating device 4, 6.

[0037] When these two differently controlled PTC heating devices 4, 6 are now combined, the diagram of FIG. 5 is obtained, in which in a first range 11, via which 0 to 50% of the heating output H of the heating arrangement 1 can be covered, exclusively the second PTC heating device 6 is subjected to a pulse width between 0≤w≤100%. By way of this a heating output H of H.sub.0≤H≤H.sub.1, can be achieved, wherein H.sub.1 corresponds to 50% of the heating output of the heating arrangement 1.

[0038] Here, the second PTC heating device 6 can be switched off or their pulse width w run down to 0% and subsequently merely the first PTC heating device 4 activated. In this case, the heating output H would remain at H.sub.1. When now the heating output is to be further increased, the first PTC heating device 4 in a second range 12 can be continued to be operated with constant voltage while the second PTC heating device 6 is subjected to a pulse width of 0%≤w≤100% and thereby a heating output H.sub.1≤H≤H.sub.2 adjusted. By way of this, a superimposition of the first PTC heating device 4 operated with constant voltage and the second PTC heating device 6 controlled with pulse width modulation occurs. By way of this, a complete coverage of a heating output curve is comparatively easily possible.

[0039] Here it is obviously conceivable that the individual first PTC heating elements 5 or the individual second PTC heating elements 7 or the first PTC heating device 4 and the second PTC heating device 6 can have different sizes or forms or the same size and the same form. Likewise it is obviously conceivable that besides the second PTC heating device 6 at least one further PTC device (not shown) is additionally arranged in the through-flow direction 8 after the second PTC heating device 6, wherein the at least one further PTC heating device comprises at least one further PTC heating element and wherein it is true that (T.sub.wRef−T.sub.2Ref) is at least >5° Celsius. By way of this, a further finer regulation of the heating output of the heating arrangement 1 is possible.

[0040] With the heating arrangement 1 according to the invention and the operating method according to the invention it is possible to reduce the dimensions of the current-carrying components, for example conductor tracks and also voltage and current peaks and thereby the vehicle electrical system load, as a result of which the entire vehicle electrical system can be designed for lower loads and thus cost-effectively. Through the individual combinability of the individual PTC heating devices 4, 6 a boost function can also be comparatively easily available for short-term maximum outputs, here through the pulse width-modulated second PTC heating device 6, without the entire vehicle electrical system having to be designed for comparatively high loads. In addition to this, a temperature and volumetric flow monitoring is also possible since the multi-stage PTC heating arrangement 1, besides the functionality of the heating, can also use the individual PTC heating elements 5, 7 as measuring elements for determining physical quantities.