SWITCHING ASSEMBLY FOR AN ELECTRIC SCREED HEATING DEVICE OF A ROAD PAVER

Abstract

A road paver comprises a tractor vehicle with a material hopper for receiving paving material and a paving screed for compacting paving material. The paving screed comprises at least one electric heating device for heating the paving screed. The road paver comprises at least one electric switching assembly configured to switch an electric power supply of the electric heating device. The electric switching assembly comprises an electric parallel circuit of two switching devices, wherein the electric parallel circuit of the two switching devices forms a series electric circuit with the electric heating device.

Claims

1. A road paver, comprising: a tractor vehicle with a material hopper for receiving paving material; a paving screed for compacting paving material, wherein the paving screed comprises an electric heating device for heating the paving screed; and an electric switching assembly configured to switch an electric power supply of the electric heating device, wherein the electric switching assembly comprises an electric parallel circuit of two switching devices, and wherein the electric parallel circuit of the two switching devices forms an electric series circuit with the electric heating device.

2. The road paver according to claim 1, wherein the two switching devices are configured to alternately supply electric power to the electric heating device.

3. The road paver according to claim 1, wherein the two switching devices are connected to a common input of the electric heating device.

4. The road paver according to claim 1, wherein the electric switching assembly is provided on the paving screed.

5. The road paver according to claim 1, wherein the two switching devices are semiconductor switching devices.

6. The road paver according to claim 1, wherein the two switching devices each comprise a transistor, a thyristor or a bidirectional thyristor diode.

7. The road paver according to claim 1, wherein the electric switching assembly is configured to supply an AC voltage to the electric heating device.

8. The road paver according to claim 7, wherein each switching device is configured to let at least one complete sine wave of the AC voltage pass in one go.

9. The road paver according to claim 7, wherein the two switching devices are configured to let successive sine waves of the AC voltage pass in an alternating manner.

10. The road paver according to claim 1, wherein the electric heating device is a resistance heating element.

11. A method for heating a paving screed of a road paver, comprising: supplying electric power to an electric resistance heating element provided on the paving screed; wherein an electric power supply to the electric resistance heating element is switched with an electric switching assembly, and wherein two switching devices of the electric switching assembly alternately supply the electric resistance heating element with electric power.

12. The method according to claim 11, wherein the electric resistance heating element is supplied with an AC voltage, and wherein a frequency of switching the supply to the electric resistance heating element between the two switching devices corresponds to a frequency of the AC voltage.

13. The method according to claim 11, wherein the electric resistance heating element is continuously supplied with electric power during the alternating power supply by the two electric switching devices.

14. A method for heating a paving screed of a road paver, the method comprising using two alternately switched switching devices in an electric switching assembly for supplying electric power to an electric heating device on the paving screed of the road paver to reduce a risk of overheating of the electric switching assembly.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In the following, an embodiment according to the disclosure is further explained.

[0029] FIG. 1 shows a schematic side view of a road paver according to an embodiment;

[0030] FIG. 2 shows a schematic top view of a road paver according to an embodiment; and

[0031] FIG. 3 shows a schematic representation of the alternating supply of the electric heating device by two switching devices connected in parallel to each other, according to an embodiment.

DETAILED DESCRIPTION

[0032] FIG. 1 shows a schematic side view of a road paver 1 according to an embodiment. The road paver 1 comprises a self-propelled tractor vehicle 3 with a material hopper 5 for receiving paving material located at the front in paving direction F. Further, an operator station 7 is provided on the tractor vehicle 3, the operator station 7 comprising input devices 8 for controlling the road paver 1 and providing space for an operator. A paving screed 9 for compacting the paving material is pulled behind the tractor vehicle 3 via drawbars 11 attached to both sides of the tractor vehicle 3. A conveyor is provided on the tractor vehicle 3 for conveying paving material from the material hopper 5 to a rear area of the road paver 1. In the rear area of the road paver 1, the paving material leaves the conveyor through a material outlet and reaches a spreading auger 13 (see FIG. 2) for distributing the paving material in front of the paving screed 9 transverse to the paving direction F.

[0033] As shown in FIG. 2, a plurality of electric heating devices 15 are provided on the paving screed 9 for electrically heating the paving screed 9. The heating devices 15 may be resistance heating elements, in particular heating rods. The heating devices 15 may be adapted to heat the paving screed 9 substantially to the temperature of the hot paving material to prevent the paving material from sticking to the paving screed 9. In the illustrated embodiment, the paving screed 9 is an extendable screed with a base screed 17 and extending units 19, 21 attached to the base screed 17 laterally on both sides with respect to the paving direction F. The extending units 19, 21 may be moved in and out to adjust the paving width. However, it may also be conceivable that the paving screed 9 comprises only the base screed 17, without any extending units 19, 21 being provided. Electric heating devices 15 may be provided both on the base screed 17 and on the extending units 19, 21.

[0034] A generator 23 is provided on the tractor vehicle 3. The generator 23 is driven by an engine 25, in particular a diesel engine, of the tractor vehicle 3 and provides electric power. The electric power from the generator 23 is used, among other things, to supply the electric heating devices 15. A power supply arrangement 27 connects the generator 23 to the electric heating devices 15 on the paving screed 9 to provide electric power to the electric heating devices 15. The power supply arrangement 27 comprises a main fuse 29 on the tractor vehicle 3. A line network 31 of the power supply arrangement 27 leads from the generator 23 via the main fuse 29 to the paving screed 9. In the illustrated embodiment, the line network 31 branches on the tractor vehicle 3 into two strands 33, 35, which are led to the paving screed 9 and supply a left screed half and a right screed half, respectively. On the paving screed 9, the line network 31 branches out further to supply the individual electric heating devices 15.

[0035] An electric switching device 37 is assigned to each of the electric heating devices 15. The electric switching assemblies 37 are each electrically connected in series with the corresponding electric heating device 15. In the illustrated embodiment, there are four electric switching assemblies 37 corresponding to the illustrated four electric heating devices 15. The electric switching assemblies 37 are each connected upstream of the corresponding electric heating device 15. The series circuits consisting of the electric switching assemblies 37 and the respective corresponding electric heating devices 15 may be connected in parallel with one another. However, it would also be conceivable that the series circuits comprising the electric switching assemblies 37 and the corresponding electric heating devices 15 are present independently of one another, for example in different circuits.

[0036] The electric switching assemblies 37 each comprise two switching devices 39 electrically connected in parallel with one another. The electric parallel circuit of the two switching devices 39 of an electric switching assembly 37 is in each case connected in series with the associated electric heating device 15. The associated electric heating device 15 comprises a common input 41 via which it is connected to both switching devices 39 of the associated electric switching assembly 37. Each switching device 39 may be set to a current-conducting state, in which a current flows through the switching device 39 that supplies electric power to the associated electric heating device 15. Each switching device 39 may be set to a non-current-conducting or blocking state, in which current flow through the electric switching device 39 to the electric heating device 15 is prevented.

[0037] For example, the two switching devices may each comprise a transistor or be formed as a transistor. In particular, the two switching devices may each comprise a bipolar transistor or be formed as a bipolar transistor. In particular, the two switching devices may each comprise an insulated gate bipolar transistor (IGBT) or be formed as an insulated gate bipolar transistor (IGBT). In particular, the two switching devices may each comprise a field-effect transistor or be formed as a field-effect transistor. For example, the two switching devices may each comprise a thyristor or be formed as a thyristor. In particular, the two switching devices may each comprise a gate turn-off thyristor (GTO) or be formed as a gate turn-off thyristor (GTO). For example, the two switching devices may each comprise a bidirectional thyristor diode (TRIAC) or be formed as a bidirectional thyristor diode (TRIAC).

[0038] Operation of the electric switching assemblies 37 is controlled by a controller 48. In the illustrated embodiment, operation of the electric switching assemblies 37 is controlled by a controller 48 provided on the tractor vehicle 3. However, the controller 48 could also be partially or fully provided on the paving screed 9. In the illustrated embodiment, the controller 48 comprises a communication module 45 that is in data exchange communication with communication modules 47 of the electric switching assemblies 37. In the illustrated embodiment, the data exchange connection between the controller 48 and the electric switching assemblies 37 runs on the line network 31 as power line communication. However, the data exchange connection could also be implemented in other ways, such as by wireless or wired data transmission. The communication modules 47 may be connected to the switching devices 39 in order to control them. The communication modules 47 may be connected to the switching devices 39 directly or via intermediate elements, such as sub-controllers. Alternatively, it might be conceivable that the switching devices 39 are connected directly (without intermediate communication modules 47) to the controller 48 or a sub-controller. For example, the switching devices 39 may be controlled via a gate connection.

[0039] The two switching devices 39 of an electric switching assembly 37 are controlled such that they alternately supply electric power to the corresponding electric heating device 15. Preferably, in operation, always one of the two switching devices 39 is in a blocking state and the other one of the two switching devices is in a current conducting state for supplying electric power to the corresponding electric heating device 15. Different timings for switching between the two switching devices 39 of an electric switching assembly 37 are conceivable. For example, when the electric heating devices 15 are supplied with an AC voltage, switching between the two switching devices 39 of an electric switching assembly 37 may be performed such that a complete sine wave of the AC voltage is passed by one of the switching devices 39 to the electric heating device 15 and the complete subsequent sine wave is then passed by the other switching device 39 to the electric heating device 15, and so on. This case is illustrated in FIG. 3, which shows a time evolution of a voltage at the input 41 of an electric heating device 15. The time intervals in which power is supplied to the electric heating device 15 via a first switching device 39 of the corresponding electric switching assembly 37 are shown in dashed lines in FIG. 3. The second switching device 39 is blocking in the corresponding time intervals. The time intervals in which power is supplied to the electric heating device 15 via the second switching device 39 of the electric switching assembly 37 are shown in solid lines in FIG. 3. In these time intervals, the first switching device 39 is blocking.

[0040] It is not mandatory that the timing of the two switching devices 39 of an electric switching assembly 37 corresponds to the situation shown in FIG. 3. In principle, the timing between a supply of the electric heating device 15 by the first switching device 39 and a supply of the electric heating device 15 by the second switching device 39 may be chosen as desired. Preferably, a frequency of the switching of the supply of the electric heating device 15 between the two switching devices 39 is in the range of a frequency of the AC electric voltage. It would, for example, also be conceivable that the switching devices 39 each let pass more than one complete sine wave of the AC voltage and only then switch over to the other switching device 39.