Switch assembly for screed electric heating device of road paver

Abstract

A road paver (1) comprises a tractor (3) having a hopper (5) for receiving paving material and a paving screed (9) for compacting the paving material. The paving screed (9) comprises at least one electric heating device (15) for heating the paving screed (9). The road paver (1) comprises at least one electric switch assembly (37) configured to switch an electric power supply of the electric heating device (15). The electric switch assembly (37) comprises an electric parallel circuit of two switch devices (39), wherein the electric parallel circuit of the two switch devices (39) forms an electric series circuit with the electric heating device (15).

Description

[0001] This application is a divisional application of Chinese invention patent application number CN202110855874.5, entitled "Switching assembly of electric heating device for screed of road paver". Technical Field

[0002] This invention relates to an electric heating system for a screed of a road paver. Background Technology

[0003] Known road pavers include a hopper located at the front of a tractor unit for holding material to be paved relative to the paving direction. During paving, the material to be paved is conveyed from the hopper via a longitudinal conveyor to the rear area of ​​the road paver. There, the paving material is distributed transversely to the paving direction by a diffuser screw propeller and thus uniformly supplied to a screed pulled by the tractor unit for compaction. It is known to heat the working parts of the screed, such as the tamping bar, screed plate, and / or pressure bar, by electricity or gas to prevent hot paving material from adhering. In the case of electric heating, resistance heating elements powered by a generator mounted on the tractor unit are distributed within the screed plate.

[0004] As recognized in EP 1 036 883 B1, operating the electric heating elements of a screed at full power for extended periods under adverse operating conditions can place significant stress on the generator and may also result in low energy efficiency. To address these issues, a timed switch for the electric heating elements of the screed is proposed. A supply line runs from the generator, located on the tractor unit, to the electric heating elements integrated into the two halves of the screed (left and right halves). Contactors are located in the supply line, thus one contactor is assigned to each screed half. The generator temperature can be monitored via temperature-dependent resistance in the generator windings. If the generator temperature exceeds a certain threshold, the operation of the screed heating elements is switched to timed control. This means, for example, that the heating element in the left half of the screed is turned off for a predetermined time period (e.g., 30 seconds), while only the heating element in the right half remains on. After the predetermined time period has elapsed, the heating element in the right half of the screed is turned off, and the heating element in the left half is turned on again. This process is repeated continuously, allowing the generator to cool down again.

[0005] A road paver is known from EP 1 295 990 B2, which includes a screed having a base screed section and extension sections on both sides of the base screed section for increasing the paving width. The screed is divided into four sections. In each section, four resistance heating elements are provided for heating their respective screed sections. The heating elements are connected to the generator of the road paver via relay switches for power supply, wherein in each case, a common relay switch is connected upstream of two adjacent heating elements. By means of a control device, if the temperature measured in a section is below a first threshold, the relay switch corresponding to the heating element of that section closes to supply power to the heating element. If the measured temperature exceeds a higher second threshold, the associated relay switch opens again to interrupt heating of that section. This is intended to maintain the screed sections within a suitable temperature range.

[0006] A road paver is known from EP 3 527 721 A1, which has multiple electric heating devices on its screed. These electric heating devices are powered by electricity supplied by a generator through a power distribution unit. The power distribution unit includes multiple power regulating devices arranged on the screed. In each case, the power regulating device is assigned to a corresponding electric heating device. The power regulating device is controlled to dynamically adjust the power supplied to each electric heating device. For example, the power regulating device may include a thyristor controller. Since the power controller generates heat during operation, it must be designed to withstand the rated power of the heating equipment, which may result in higher costs, especially for larger rated power. Summary of the Invention

[0007] The purpose of this invention is to provide an economical and low-maintenance power supply for a heating system for ironing boards in a simple manner.

[0008] The road paver according to the invention includes a tractor having a hopper for receiving paving material and a paving screed for compacting the paving material. The paving screed includes at least one electric heating device for heating the paving screed. The paver includes at least one electric switching assembly configured to switch the power supply to the electric heating device. The electric switching assembly includes an electrically parallel circuit of two switching devices. The electrically parallel circuit of the two switching devices forms an electrically series circuit with the electric heating device.

[0009] Because the two switching devices are connected in parallel, power can be supplied to the electric heating device even if one of the switching devices does not allow current to flow. Therefore, the current does not need to flow continuously through both switching devices during the operation of the heating device. If the switching devices do not need to be continuously energized during the operation of the electric heating device, a switching device with a lower rated current (based on continuous operation) can be used. If the switching devices do not need to be continuously energized during the operation of the electric heating device, the heating load on the switching devices during operation can be reduced. Cost savings can be achieved by using two "smaller" size switching devices compared to using one "larger" switching device. Because the parallel circuit of the two switching devices forms a series circuit with the electric heating device, the electric heating device can operate in the same way regardless of which of the two switching devices the current flows through.

[0010] Two switching devices can be configured to alternately supply power to the electric heating device. For example, these two switching devices can be controlled by the control unit of a road paver to alternately supply power to the electric heating device. When the two switching devices alternately supply power to the electric heating device, they can alternately conduct and not conduct current. If one of the switching devices heats up during the conducting phase, it can be cooled to at least a certain degree during the subsequent non-conducting phase without terminating, interrupting, and / or damaging the operation of the electric heating device. This can offset damage to the switching equipment due to overheating.

[0011] Two switching devices can be connected to the common input terminal of the electric heating device. An electric switching assembly with two switching devices connected in parallel can be used with a conventional electric heating device that has only one input. The operation of the electric heating device is independent of which of the two switching devices provides current.

[0012] The electrical switch assembly can be mounted on the screed. It is particularly preferable to provide the electrical switch assembly on the screed if multiple electric heating devices for heating the screed are installed on it, with each electric heating device assigned its own electrical switch assembly. Mounting the electrical switch assembly on the screed simplifies the electrical connection between the screed and the tractor.

[0013] The two switching devices can be semiconductor switching devices. Because semiconductor switching devices are sensitive to temperature, it is particularly important to connect two switching devices in parallel to supply power to the electric heating device to prevent overheating. The semiconductor switching devices can be configured to variably regulate the power supplied to the electric heating device.

[0014] The two switching devices may each include a transistor or be formed as a transistor. Specifically, the two switching devices may each include a bipolar transistor or be formed as a bipolar transistor. Specifically, the two switching devices may each include an insulated-gate bipolar transistor (IGBT) or be formed as an insulated-gate bipolar transistor (IGBT). Specifically, the two switching devices may each include a field-effect transistor or be formed as a field-effect transistor. The two switching devices may each include a thyristor or be formed as a thyristor. Specifically, the two switching devices may each include a gate-off thyristor (GTO) or be formed as a gate-off thyristor (GTO). The two switching devices may each include a bidirectional thyristor diode (TRIAC) or be formed as a bidirectional thyristor diode (TRIAC).

[0015] The electrical switching assembly can be configured to supply AC voltage to the electric heating device. The AC voltage can be provided by the generator of the road paver.

[0016] Each of the two switching devices can be configured to allow at least one complete sine wave of the AC voltage to pass through at once. Each of the two switching devices can be configured to operate the electric heating device alone (without the other switching device) for at least a finite period of time. Each of the two switching devices can be configured to allow fewer than 100, 80, 50, 40, 20, 10, 5, or 2 complete sine waves of the AC voltage to pass through at once. Each of the two switching devices can be configured to allow at least one, at least two, at least five, at least ten, or at least 20 complete sine waves of the AC voltage to pass through at once. By limiting the duration of current flow through a single switching device, the heating of the switching device can be effectively limited.

[0017] The two switching devices can be configured to allow a continuous sinusoidal wave of AC voltage to pass through alternately.

[0018] An electric heating device can be a resistive element. An electric heating device can be a heating rod.

[0019] The present invention also relates to a method for heating a screed of a road paver. The method includes supplying electricity to at least one resistance heating element disposed on the screed. The power supply to the resistance heating element is switched by an electrical switching assembly. The electrical switching assembly includes two switching devices. The two switching devices of the electrical switching assembly alternately supply power to the resistance heating element.

[0020] When the two switching devices of the electrical switching assembly alternately supply power to the resistance heating element, one of the switching devices may have no current flowing through it while the other switching device does. When the resistance heating element is powered by the other switching device, the switching device without current flowing through it has a chance to cool down.

[0021] The resistance heating element can be supplied with AC voltage.

[0022] The frequency at which the supply of power to the resistance heating element is switched between the two switching devices can correspond to the frequency of the AC voltage. The frequency at which the supply of power to the resistance heating element is switched between the two switching devices can also be less than the frequency of the AC voltage.

[0023] The resistance heating element can be continuously powered during the alternating power supply of two electrical switching devices.

[0024] The present invention also relates to the use of two alternating switching devices in an electrical switching assembly for supplying power to an electric heating device on the screed of a paving finishing machine, thereby reducing the risk of overheating of the electrical switching assembly.

[0025] Because the two switching devices switch alternately, one of the switching devices will cool down, while the other switching device supplies power to the electric heating device.

[0026] As described above, according to one aspect, the present invention provides a road paver; according to another aspect, a method for heating the screed of the road paver; and according to yet another aspect, the invention provides the use of two alternating switching devices. Features, advantages, and explanations described with respect to one of these aspects may be transferred to the other aspects. Attached Figure Description

[0027] The invention is further illustrated below by way of an embodiment.

[0028] Figure 1 A schematic side view of a road paver according to an embodiment is shown; Figure 2 A schematic top view of a road paver according to an embodiment is shown; and Figure 3 A schematic diagram is shown, according to an embodiment, of two switching devices connected in parallel to alternately supply electric heating to the heating device. Detailed Implementation

[0029] Figure 1A schematic side view of a road paver 1 according to an embodiment is shown. The road paver 1 includes a self-propelled tractor 3 having a hopper 5 for receiving paving material, the hopper 5 being located at the front in the paving direction F. Furthermore, an operating station 7 is provided on the tractor 3, the operating station 7 including input devices 8 for controlling the road paver 1 and providing space for the operator. A paving screed 9 for compacting the paving material is pulled behind the tractor 3 via drawbars 11 attached to both sides of the tractor 3. A conveyor is provided on the tractor 3 for conveying the paving material from the hopper 5 to the rear region of the road paver 1. In the rear region of the road paver 1, the paving material leaves the conveyor through a discharge port and reaches a diffuser auger propeller 13 (see FIG. 2) for distributing the paving material transversely to the paving direction F in front of the paving screed 9.

[0030] like Figure 2 As shown, 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 can be resistance heating elements, particularly heating rods. The heating devices 15 are 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 having a base screed 17 and extension units 19, 21, which are laterally attached to the base screed 17 on both sides relative to the paving direction F. The extension units 19, 21 can be moved in and out to adjust the paving width. However, it is also conceivable that the paving screed 9 only includes the base screed 17 without any extension units 19, 21. The electric heating devices 15 can be provided on both the screed 17 and the extension units 19, 21.

[0031] A generator 23 is mounted on the tractor unit 3. The generator 23 is driven and powered by the engine 25 of the tractor unit 3, particularly a diesel engine. The power from the generator 23 is used specifically to supply the electric heating device 15. A power supply unit 27 connects the generator 23 to the electric heating device 15 on the screed 9 to supply power to the electric heating device 15. The power supply unit 27 includes a main fuse 29 on the tractor unit 3. A wiring network 31 of the power supply unit 27 extends from the generator 23 via the main fuse 29 to the screed 9. In the illustrated embodiment, the wiring network 31 branches into two lines 33 and 35 on the tractor unit 3, which are guided to the screed 9 and supply power to the left and right halves of the screed, respectively. On the screed 9, the wiring network 31 further branches to supply individual electric heating devices 15.

[0032] An electrical switching device 37 is assigned to each electric heating device 15. Each electrical switching assembly 37 is connected in series with its corresponding electric heating device 15. In the illustrated embodiment, there are four electrical switching assemblies 37 corresponding to the four electric heating devices 15 shown. Each electrical switching assembly 37 is connected upstream of its corresponding electric heating device 15. The series circuit consisting of the electrical switching assembly 37 and its respective corresponding electric heating device 15 can be connected in parallel with each other. However, it is also conceivable that the series circuit including the electrical switching assembly 37 and its corresponding electric heating device 15 may exist independently of each other, for example, in different circuits.

[0033] Each electrical switch assembly 37 includes two switching devices 39 electrically connected in parallel with each other. The parallel circuit of the two switching devices 39 of each electrical switch assembly 37 is connected in series with the associated electric heating device 15 in each case. The associated electric heating device 15 includes a common input 41, through which it is connected to the two switching devices 39 of the associated electrical switch assembly 37. Each switching device 39 can be configured to a current-conducting state, wherein current flows through the switching device 39, which supplies power to the associated electric heating device 15. Each switching device 39 can be configured to a non-conducting state or a blocking state, wherein current flowing through the electrical switching device 39 to the electric heating device 15 is blocked.

[0034] For example, these two switching devices may each include a transistor or be formed as a transistor. Specifically, these two switching devices may each include a bipolar transistor or be formed as a bipolar transistor. Specifically, these two switching devices may each include an insulated-gate bipolar transistor (IGBT) or be formed as an insulated-gate bipolar transistor (IGBT). Specifically, these two switching devices may each include a field-effect transistor or be formed as a field-effect transistor. For example, these two switching devices may each include a thyristor or be formed as a thyristor. Specifically, these two switching devices may each include a gate-off thyristor (GTO) or be formed as a gate-off thyristor (GTO). For example, these two switching devices may each include a bidirectional thyristor diode (TRIAC) or be formed as a bidirectional thyristor diode (TRIAC).

[0035] The operation of the electrical switch assembly 37 is controlled by the controller 48. In the illustrated embodiment, the operation of the electrical switch assembly 37 is controlled by the controller 48 located on the tractor 3. However, the controller 48 may also be partially or wholly located on the screed 9. In the illustrated embodiment, the controller 48 includes a communication module 45 that exchanges data with the communication module 47 of the electrical switch assembly 37. In the illustrated embodiment, the data exchange connection between the controller 48 and the electrical switch assembly 37 operates on a line network 31, which serves as power line communication. However, the data exchange connection may also be implemented in other ways, such as via wireless or wired data transmission. The communication module 47 may be connected to the switching devices 39 to control them. The communication module 47 may be directly connected to or connected to the switching devices 39 via an intermediate element such as a sub-controller. Alternatively, it is conceivable that the switching devices 39 may be directly connected (without the intermediate communication module 47) to the controller 48 or a sub-controller. For example, the switching devices 39 may be controlled via a gate connection.

[0036] The two switching devices 39 of the electrical switching assembly 37 are controlled to alternately supply power to the corresponding electric heating device 15. Preferably, in operation, one of the two switching devices 39 is always in an blocking state, while the other of the two switching devices is in a current-conducting state for supplying power to the corresponding electric heating device 15. Different timing arrangements for switching between the two switching devices 39 of the electrical switching assembly 37 are conceivable. For example, when the electric heating device 15 is supplied with AC voltage, switching can be made between the two switching devices 39 of the electrical switching assembly 37 so that a complete sine wave of the AC voltage is transmitted to the electric heating device 15 by one switching device 39, and then a subsequent complete sine wave is transmitted to the electric heating device 15 by the other switching device 39, and so on. This situation is... Figure 3 The diagram shows the time evolution of the voltage at input terminal 41 of the electric heating device 15. The time interval for supplying power to the electric heating device 15 via the first switching device 39 of the corresponding electric switching assembly 37 is shown in [the diagram / illustration]. Figure 3 The second switching device 39 is blocked within a corresponding time interval. The time interval for supplying power to the electric heating device 15 through the second switching device 39 of the electric switching assembly 37 is... Figure 3 The first switching device 39 is blocked during these time intervals, as shown by solid lines.

[0037] The timing arrangement of the two switching devices 39 of the electrical switching assembly 37 corresponds to Figure 3The situation shown is not mandatory. In principle, the timing between supplying the electric heating device 15 by the first switching device 39 and the second switching device 39 can be selected as needed. Preferably, the frequency of switching the supply of the electric heating device 15 between the two switching devices 39 is within the frequency range of the AC voltage. For example, it is also conceivable that each switching device 39 allows more than one complete sine wave of the AC voltage to pass through before switching to the other switching device 39.

Claims

1. A road paver, comprising: A tractor unit, which has a hopper for holding paving materials; A screed for compacting paving materials, wherein the screed includes an electric heating device for heating the screed. An electric switching assembly configured to switch the power supply to the electric heating device, wherein the electric switching assembly includes an electrically parallel circuit of two switching devices, and wherein the electrically parallel circuit of the two switching devices forms an electrically 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 power to the electric heating device.

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

4. The road paver according to claim 1, wherein, The electrical switch assembly is mounted on the screed board.

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 respectively include a transistor, a thyristor, or a bidirectional thyristor diode.

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

8. The road paver according to claim 1, wherein, The electrical switch assembly is configured to supply AC voltage to the electric heating device.

9. The road paver according to claim 8, wherein, Each switching device is configured to allow at least one complete sine wave of AC voltage to pass through at once.

10. The road paver according to claim 8, wherein, The two switching devices are configured to allow a continuous sinusoidal wave of AC voltage to pass through alternately.

11. A method for heating the screed of a road paver, comprising: Power is supplied to the resistance heating element disposed on the screed. The power supply to the resistance heating element is switched by a power switch assembly, wherein the two switching devices of the power switch assembly alternately supply power to the resistance heating element.

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

13. The method according to claim 11, characterized in that, The resistance heating element is continuously supplied with power during the alternating power supply from two electrical switching devices.

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

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