Switching assembly for electric heating device of road paving screed in road paving machinery

Abstract

To provide a power supply of an electric heating system of a paving screed that is economical with low-maintenance by simple means.SOLUTION: A road paving machine 1 comprises a tractor 3 with a material hopper 5 for receiving a pavement material, and a paving screed 9 for compacting the pavement material. The paving screed 9 comprises at least one electric heating apparatus 15 for heating the paving screed 9. The road paving machine 1 comprises at least one electric switching assembly 37 configured to switch power supply to the electric heating apparatus 15. The electric switching assembly 37 comprises a parallel electric circuit of two switching elements 39, and the parallel electric circuit of the two switching elements 39 and the electric heating apparatus 15 form a serial electric circuit.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to electric heating of a paving screed of a road paving machine.

Background Art

[0002] A known road paving machine includes a material hopper for receiving a paving material in front of a tractor of the road paving machine in the paving progress direction. During paving, the paving material is conveyed from the material hopper to the rear of the road paving machine via a front-rear conveying device. Here, since the paving material is diffused in the lateral direction with respect to the paving progress direction using a spreading auger, it is uniformly supplied to a paving screed towed by a tractor to compress the paving material. It is known to electrically heat or heat using gas the working parts of the paving screed, such as a tamper bar, a screed plate, and / or a press bar, to prevent the high-temperature paving material from sticking. In the case of electric heating, a resistance heating element supplied with electric power by a generator provided on the tractor is arranged so as to spread over the paving screed.

[0003] European Patent No. 1036883 discloses that continuously operating the electric heating elements of a pavement screed at full power can place a heavy load on the generator under unfavorable operating conditions and result in low energy efficiency. To solve this problem, it is proposed to periodically switch the electric heating elements of the pavement screed on and off. A supply line runs from a generator on the tractor to electric heating elements integrated into the two halves of the pavement screed (left and right halves). The supply line is equipped with contactors, with one contactor assigned to each half of the screed. The generator temperature is monitored using temperature-dependent resistors installed in the generator windings. When the generator temperature exceeds a certain threshold, the operation of the pavement screed heating elements is switched to clockwise operation. This means, for example, that the heating element of the left half of the screed is switched off for a predetermined period, e.g., 30 seconds, while only the heating element of the right half of the screed remains switched on. After a predetermined time has elapsed, the heating element on the right half of the screed is switched off, and the heating element on the left half of the screed is switched on again. This process is continuously repeated, allowing the generator to be cooled again.

[0004] European Patent No. 1295990 discloses a road paving machine having a paving screed having a base screed portion and extensions provided on both sides of the base screed portion to widen the pavement width. The paving screed is divided into four sections. Each section is provided with four resistance heating elements for heating the associated screed section. The heating elements are connected to the generator of the road paving machine via relay switches for power supply, and a common relay switch is connected to the upstream side of two adjacent heating elements. The control unit closes the relay switch corresponding to the heating element in the section to supply power to the heating element when the temperature measured in the section falls below a first threshold. When the measured temperature exceeds a higher second threshold, the associated relay switch is opened again to interrupt heating of the section. This is to maintain the screed section within an appropriate temperature range.

[0005] European Patent No. 3527721 discloses a road paving machine equipped with a paving screed having multiple electric heating devices. Power generated by a generator is supplied to the electric heating devices by a power distribution unit. The power distribution unit comprises multiple power adjusters mounted on the paving screed. Each power adjuster is assigned to a corresponding electric heating device. The power adjusters are controlled to individually and dynamically adjust the power supplied to each associated electric heating device. The power adjusters may include, for example, thyristor controllers. Because the power controllers generate heat during operation, they must be designed to match the rated power of the electric heating devices, which can lead to increased costs, especially when the rated power is high. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] European Patent No. 1036883 [Patent Document 2] European Patent No. 1295990 [Patent Document 3] European Patent No. 3527721 [Overview of the project] [Problems that the invention aims to solve]

[0007] The objective of the present invention is to provide a power source for an economical and low-maintenance electric heating system for pavement screeds by simple means.

[0008] This objective is achieved by the road paving machine described in claim 1, the method for heating the paving screed of the road paving machine described in claim 11, and the use described in claim 14. Dependent claims illustrate preferred embodiments of the present invention. [Means for solving the problem]

[0009] The road paving machine according to the present invention comprises a tractor having a material hopper for receiving paving material and a paving screed for compressing the paving material. The paving screed comprises at least one electric heating device for heating the paving screed. The paving machine comprises at least one electric switching assembly configured to turn on and off the power supply to the electric heating device. The electric switching assembly comprises a parallel electrical circuit of two switching elements. The parallel electrical circuit of the two switching elements forms a series electrical circuit with the electric heating device.

[0010] Because the two switching elements are connected in parallel, power can be supplied to the electric heating device even if one of the switching elements is in a non-conductive state. Therefore, it is not necessary to continuously supply current to both switching elements while the electric heating device is operating. If it is not necessary to continuously supply current to the switching elements while the electric heating device is operating, a switching element with a smaller rated current (based on continuous operation) can be used. If it is not necessary to continuously supply current to the switching elements while the electric heating device is operating, heating of the switching elements during operation can be reduced. By using two "smaller" switching elements, cost reductions can be achieved compared to using one "larger" switching element. In addition, since the parallel electrical circuit of the two switching elements forms a series electrical circuit with the electric heating device, the electric heating device can be operated in the same way regardless of which of the two switching elements the current flows through.

[0011] Two switching elements can be configured to alternately supply power to an electric heating device. For example, the control unit of a road paving machine can control the two switching elements to alternately supply power to an electric heating device. When the two switching elements alternately supply power to the electric heating device, the two switching elements alternately enter the conductive and non-conductive states. Even if one of the switching elements is heated during the conductive phase, it can be cooled at least to some extent during the subsequent non-conductive phase without terminating, interrupting, and / or impairing the operation of the electric heating device. This helps to suppress damage to the switching elements due to overheating.

[0012] The two switching elements may be connected to a common input of the electric heating device. An electric switching assembly in which the two switching elements are connected in parallel can be used in conventional electric heating devices that have only one input. The operation of the electric heating device is not affected by which of the two switching elements is supplying power.

[0013] The electrical switching assembly may be installed on the pavement screed. It is particularly preferable to install the electrical switching assembly on the pavement screed if multiple electric heating devices for heating the pavement screed are installed on the pavement screed, and one electrical switching assembly is assigned to each of them. Installing the electrical switching assembly on the pavement screed simplifies the electrical connection between the pavement screed and the tractor.

[0014] The two switching elements may be semiconductor switching elements. Since semiconductor switching elements are relatively temperature-sensitive, it is particularly relevant to avoid overheating by connecting two switching elements in parallel to supply power to the electric heating device. The semiconductor switching elements can be configured to variably adjust the power supply to the electric heating device.

[0015] Each of the two switching elements may comprise a transistor, or can be formed as a transistor. In particular, each of the two switching elements may comprise a bipolar transistor, or can be formed as a bipolar transistor. In particular, each of the two switching elements may comprise an insulated-gate bipolar transistor (IGBT), or can be formed as an insulated-gate bipolar transistor (IGBT). In particular, each of the two switching elements may comprise a field-effect transistor, or can be formed as a field-effect transistor. Each of the two switching elements may comprise a thyristor, or can be formed as a thyristor. In particular, each of the two switching elements may comprise a gate-turn-off thyristor (GTO), or can be formed as a gate-turn-off thyristor (GTO). Each of the two switching elements may comprise a bidirectional thyristor diode (TRIAC), or can be formed as a bidirectional thyristor diode (TRIAC).

[0016] The electrical switching assembly can be configured to supply AC voltage to an electric heating device. The AC voltage can be supplied by a generator on a road paving machine.

[0017] Each of the two switching elements can be configured to pass at least one complete sine wave of AC voltage at a time. Each of the two switching elements can be configured to operate an electric heating device independently (without using other switching elements) at least temporarily. Each of the two switching elements can be configured to pass at least 100, 80, 40, 20, 10, 5, or 2 complete sine waves of AC voltage at a time. Each of the two switching elements can be configured to pass at least 1, 2, 5, 10, or 20 complete sine waves of AC voltage at a time. By limiting the time that current flows through one switching element, the heating of the switching element can be effectively limited.

[0018] The two switching elements can be configured to alternately pass a continuous sinusoidal wave of AC voltage through them.

[0019] The electric heating device may be a resistance heating element. The electric heating device may be a heating rod.

[0020] The present invention also relates to a method for heating a paving screed of a road paving machine. This method includes supplying power to at least one electrical resistance heating element provided in the paving screed. The power supply to the electrical resistance heating element is switched on and off by an electrical switching assembly. The electrical switching assembly comprises two switching elements. The two switching elements of the electrical switching assembly alternately supply power to the electrical resistance heating element.

[0021] When two switching elements in an electrical switching assembly alternately supply power to an electrical resistance heating element, one of the two switching elements can be de-energized while the other switching element is energized. The de-energized switching element can be cooled while the other switching element is supplying power to the electrical resistance heating element.

[0022] An alternating voltage may be supplied to the electric resistance heating element.

[0023] The frequency for switching the power supply to the electric resistance heating element between two switching elements may correspond to the frequency of the alternating voltage. Also, the frequency for switching the power supply to the electric resistance heating element between two switching elements may be smaller than the frequency of the alternating voltage.

[0024] The electric resistance heating element can continuously receive power supply while the two switching elements supply power alternately.

[0025] The present invention also relates to the use of two switching elements that are alternately switched to reduce the overheating risk of an electric switching assembly in an electric switching assembly for supplying power to an electric heating device on a paving screed of a road paving machine.

[0026] Since the two switching elements are alternately switched, while one switching element supplies power to the electric heating device, the other switching element can be cooled.

[0027] As described above, in one aspect, the present invention provides a road paving machine, in another aspect, provides a method for heating a paving screed of a road paving machine, and in still another aspect, provides the use of switching elements that are alternately switched. The features, advantages, and explanations described in relation to these aspects can also be transferred to other aspects. [[ID=2!4]]

Brief Description of the Drawings

[0028] [Figure 1] It is a schematic side view of a road paving machine according to an embodiment of the present invention. [Figure 2] It is a schematic plan view of a road paving machine according to an embodiment of the present invention. [Figure 3]This is a schematic diagram illustrating the alternating power supply to an electric heating device by two switching elements connected in parallel, according to one embodiment of the present invention. [Modes for carrying out the invention]

[0029] The present invention will be further described below based on embodiments.

[0030] Figure 1 is a schematic side view of a road paving machine 1 according to one embodiment of the present invention. The road paving machine 1 comprises a self-propelled tractor 3 having a material hopper 5 positioned forward in the paving direction F for receiving paving material. The tractor 3 is also provided with an operator's console 7, which has an input device 8 for controlling the road paving machine 1 and provides space for an operator. A paving screed 9 for compressing the paving material is towed at the rear of the tractor 3 via tow bars 11 attached to both sides of the tractor 3. The tractor 3 is equipped with a conveying device for transporting paving material from the material hopper 5 to the rear of the road paving machine 1. The paving material exits the conveying device through a material outlet and reaches a diffusion auger 13 (see Figure 2) at the rear of the road paving machine 1, which diffuses the paving material in front of the paving screed 9 in a direction transverse to the paving direction F.

[0031] As shown in Figure 2, a plurality of electric heating devices 15 are provided on the pavement screed 9 to electrically heat the screed 9. The electric heating devices 15 may be resistance heating elements, particularly heating rods. The electric heating devices 15 can be configured to heat the pavement screed 9 to substantially the temperature of the high-temperature pavement material in order to prevent the pavement material from sticking to the screed 9. In the illustrated embodiment, the pavement screed 9 is an extendable screed comprising a base screed 17 and extensions 19, 21 attached to both lateral sides of the base screed 17 with respect to the pavement direction of travel F. The extensions 19, 21 can be extended and retracted to adjust the pavement width. However, the pavement screed 9 may also consist only of the base screed 17, without the extensions 19, 21. The electric heating devices 15 may be provided on both the base screed 17 and the extensions 19, 21.

[0032] The tractor 3 is equipped with a generator 23. The generator 23 is driven by the engine 25 of the tractor 3, specifically a diesel engine, and supplies power. The power from the generator 23 is used to supply power to the electric heating devices 15 in particular. A power supply unit 27 connects the generator 23 to the electric heating devices 15 on the pavement screed 9, thereby supplying power to the electric heating devices 15. The power supply unit 27 is equipped with a main fuse 29 located in the tractor 3. The wiring network 31 of the power supply unit 27 connects from the generator 23 to the pavement screed 9 via the main fuse 29. In the illustrated embodiment, the wiring network 31 branches on the tractor 3 into two strands 33, 35, which are led to the pavement screed 9, supplying power to the left half and right half of the screed, respectively. On the pavement screed 9, the wiring network 31 further branches to supply power to the individual electric heating devices 15.

[0033] Each electric heating device 15 is assigned one electric switching assembly 37. Each electric switching assembly 37 is electrically connected in series with the corresponding electric heating device 15. In the illustrated embodiment, four electric switching assemblies 37 correspond to four illustrated electric heating devices 15. Each electric switching assembly 37 is connected upstream of the corresponding electric heating device 15. The series circuits consisting of the electric switching assemblies 37 and their respective electric heating devices 15 may be connected in parallel with each other. However, the series circuits consisting of the electric switching assemblies 37 and their corresponding electric heating devices 15 may be provided independently of each other, for example, in different circuits.

[0034] Each electrical switching assembly 37 comprises two switching elements 39 electrically connected in parallel to each other. The parallel electrical circuits of the two switching elements 39 of the electrical switching assembly 37 are each connected in series with an associated electric heating device 15. The associated electric heating device 15 has a common input 41 through which it is connected to both switching elements 39 of the associated electrical switching assembly 37. Each switching element 39 may be set to a conducting state so that current flows through the switching element 39 to supply power to the associated electric heating device 15. Each switching element 39 may be set to a non-conducting state or a blocked state so that the flow of current through the switching element 39 to the electric heating device 15 is blocked.

[0035] For example, each of the two switching elements may include a transistor, or can be formed as a transistor. In particular, each of the two switching elements may include a bipolar transistor, or can be formed as a bipolar transistor. In particular, each of the two switching elements may include an insulated-gate bipolar transistor (IGBT), or can be formed as an insulated-gate bipolar transistor (IGBT). In particular, each of the two switching elements may include a field-effect transistor, or can be formed as a field-effect transistor. For example, each of the two switching elements may include a thyristor, or can be formed as a thyristor. In particular, each of the two switching elements may include a gate-turn-off thyristor (GTO), or can be formed as a gate-turn-off thyristor (GTO). For example, each of the two switching elements may include a bidirectional thyristor diode (TRIAC), or can be formed as a bidirectional thyristor diode (TRIAC).

[0036] The operation of the electrical switching assembly 37 is controlled by a controller 48. In the illustrated embodiment, the operation of the electrical switching assembly 37 is controlled by a controller 48 located on the tractor 3. However, the controller 48 may be located on the pavement screed 9, either partially or entirely. In the illustrated embodiment, the controller 48 includes a communication module 45 that performs data exchange communication with a communication module 47 of the electrical switching assembly 37. In the illustrated embodiment, the data exchange connection between the controller 48 and the electrical switching assembly 37 is performed over a wiring network 31 as power line communication. However, the data exchange connection can also be performed by other means, such as wireless or wired data transmission. The communication module 47 can be connected to the switching element 39 to control the switching element 39. The communication module 47 can be connected to the switching element 39 directly or via an intermediate element such as a subcontroller. Alternatively, the switching element 39 may be connected directly (without the communication module 47 in between) to the controller 48 or subcontroller. The switching element 39 can be controlled, for example, via a gate connection.

[0037] The two switching elements 39 of the electrical switching assembly 37 are controlled to alternately supply power to the corresponding electric heating device 15. Preferably, during operation, one of the two switching elements 39 is always in an off state, and the other switching element 39 is in a conductive state to supply power to the corresponding electric heating device 15. Various timings are possible for switching the two switching elements 39 of the electrical switching assembly 37. For example, when supplying an AC voltage to the electric heating device 15, the switching between the two switching elements 39 of the electrical switching assembly 37 may be performed such that one complete sine wave of the AC voltage is transmitted to the electric heating device 15 by one switching element 39, and the subsequent complete sine wave is transmitted to the electric heating device 15 by the other switching element 39. This example is shown in Figure 3, which shows the time variation of the voltage at the input 41 of the electric heating device 15. The time intervals in which power is supplied to the electric heating device 15 via the first switching element 39 of the corresponding electrical switching assembly 37 are shown by dashed lines in Figure 3. During these time intervals, the second switching element 39 is off. The time intervals in which power is supplied to the electric heating device 15 via the second switching element 39 of the electric switching assembly 37 are shown by solid lines in Figure 3. During these time intervals, the first switching element 39 is off.

[0038] Note that the switching timing of the two switching elements 39 of the electrical switching assembly 37 does not have to be the same as that shown in Figure 3. In principle, the timing of power supply to the electric heating device 15 by the first switching element 39 and the power supply to the electric heating device 15 by the second switching element 39 can be arbitrarily selected. Preferably, the switching frequency of power supply to the electric heating device 15 between the two switching elements 39 is within the range of the AC voltage frequency. For example, it is conceivable that each switching element 39 may pass one or more complete sine waves of AC voltage through before switching to the other switching element 39.

Claims

1. A tractor (3) having a material hopper (5) for receiving paving material, A pavement screed (9) for compressing pavement material, A road paving machine (1) equipped with, The pavement screed (9) is equipped with at least one electric heating device (15) for electrically heating the pavement screed (9), The electric heating device (15) is provided with at least one electrical switching assembly (37) configured to turn on and off the power supply to the electric heating device (15), The electrical switching assembly (37) comprises a parallel electrical circuit of two switching elements (39), and the parallel electrical circuit of the two switching elements (39) forms a series electrical circuit with the electric heating device (15). A road paving machine characterized by the following features.

2. The road paving machine according to claim 1, wherein the two switching elements (39) are configured to alternately supply power to the electric heating device (15).

3. The road paving machine according to claim 1 or 2, wherein the two switching elements (39) are connected to the common input of the electric heating device (15).

4. The road paving machine according to any one of claims 1 to 3, wherein the electrical switching assembly (37) is provided on the paving screed (9).

5. The road paving machine according to any one of claims 1 to 4, wherein the two switching elements (39) are semiconductor switching elements.

6. The road paving machine according to any one of claims 1 to 5, wherein each of the two switching elements (39) comprises a transistor, a thyristor, or a bidirectional thyristor diode.

7. The road paving machine according to any one of claims 1 to 6, wherein the electrical switching assembly (37) is configured to supply an AC voltage to the electric heating device (15).

8. The road paving machine according to claim 7, wherein each switching element (39) is configured to pass at least one complete sinusoidal wave of an alternating voltage at once.

9. The road paving machine according to claim 7 or 8, wherein the two switching elements (39) are configured to alternately pass a continuous sinusoidal wave of AC voltage.

10. The road paving machine according to any one of claims 1 to 9, wherein the electric heating device (15) is a resistance heating element.

11. A method for heating the paving screed (9) of a road paving machine (1), Power is supplied to at least one electrical resistance heating element (15) provided in the pavement screed (9), The power supply to the electrical resistance heating element (15) is switched on and off by the electrical switching assembly (37). The electrical switching assembly (37) comprises a parallel electrical circuit of two switching elements (39), and the parallel electrical circuit of the two switching elements (39) forms a series electrical circuit with the electrical resistance heating element (15). The two switching elements (39) of the electrical switching assembly (37) alternately supply power to the electrical resistance heating element (15). A method characterized by the following:

12. The method according to claim 11, wherein the electrical resistance heating element (15) is supplied with an AC voltage, and the frequency at which the power supply to the electrical resistance heating element (15) is switched between the two switching elements (39) corresponds to the frequency of the AC voltage.

13. The method according to claim 11 or 12, wherein the electrical resistance heating element (15) is continuously supplied with power while the two switching elements (39) alternately supply power.

14. A method for heating the paving screed (9) of a road paving machine (1), By using two alternately switching elements (39) in an electrical switching assembly (37) for supplying power to an electric heating device (15) on the paving screed (9) of a road paving machine (1), the risk of damage due to overheating of the two switching elements (39) in the electrical switching assembly (37) is reduced. A method wherein the parallel electrical circuit of the two switching elements (39) forms a series electrical circuit with the electric heating device (15).

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