GB2438712A

GB2438712A - Device for breaking and closing electric circuits

Info

Publication number: GB2438712A
Application number: GB0709449A
Authority: GB
Inventors: Natali Gianfranco
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-05-31
Filing date: 2007-05-17
Publication date: 2007-12-05
Anticipated expiration: 2027-05-17
Also published as: GB2438712B; GB0709449D0; ITVR20060096A1

Abstract

A device for breaking and closing electric circuits, having its own rated operating current and comprising a plurality of parallel branches (5) electrically connected between a first equipotential section (3) and a second equipotential section (4). Each branch having at least one controlled switch (6) and at least one fuse (7) mounted in series with one another. The fuse (7) of each branch (5) has its own tripping current which is lower than the rated current of the breaking device (1), whilst the switches (6) of the individual branches (5) are controlled substantially in a synchronised way.

Description

Device for breaking and closing electric circuits The present invention

relates to a device for breaking and closing electric circuits in particular intended for the power supply electric circuits of electric motors (for example of hydraulic power units) Circuits for supplying electrical loads usually comprise, as a breaking and closing device, a switch able to interrupt both the circuit rated current and any short circuit current present.

In most applications, the switch consists of a remote control switch, which allows remote activation.

However, the prior art has several disadvantages.

During circuit operation (and in particular at the moment when the circuit is broken or closed), faults may arise in the switch which prevent it from opening (for example remote control switch contacts sticking due to the high operating currents) When that happens, at the moment when the circuit breaking command is given, the remote control switch cannot break the circuit and therefore the load continues to be supplied.

However, failure to break the circuit may both endanger operators (for example if the circuit is used for moving movable parts which therefore would not stop), and be a possible cause of a system fault (for example if a motor keeps trying to operate even after the end of a stroke has been reached, with consequent overheating) To avoid such disadvantages there is therefore a known technique of associating with the circuit for the supply of electrical loads, safety devices which allow the circuit to be broken, automatically or manually, should the remote control switch malfunction.

In the most widespread embodiment, the safety device consists of a second remote control switch identical to the first and placed in series with it.

However, said embodiment has the disadvantage of leading to a doubling of the device production costs, since it requires two identical switches, one of which remains unused for most of the time.

In this situation, the technical purpose which forms the basis of the present invention is to provide a device for breaking and closing electric circuits which overcomes the above-mentioned disadvantages.

In particular, the technical purpose of the present invention is to provide a device for breaking and closing electric circuits which allows the circuit to be broken even in the event of a fault.

The present invention also has for a technical purpose to provide a device for breaking and closing electric circuits with limited cost.

The technical purpose specified and the aims indicated are substantially achieved by a device for breaking and closing electric circuits as described in the claims herein.

Further features and advantages of the present invention are more apparent in the detailed

description below, with reference to several

preferred, non-limiting embodiments of a device for breaking and closing electric circuits, illustrated in the accompanying drawings, in which: -Figure 1 is a schematic view of a device for breaking and closing electric circuits made in accordance with the present invention; -Figure 2 is a circuit diagram of a possible embodiment of the device for breaking and closing electric circuits in accordance with the present invention; -Figure 3 is a circuit diagram of a control and check circuit of the device for breaking and closing electric circuits illustrated in Figure 2; -Figure 4 is an axonometric view of an embodiment of a device for breaking and closing electric circuits made in accordance with the present invention, with some parts cut away to better illustrate others; -Figure 5 is an enlarged view of the detail V from Figure 4; -Figure 6 is a top view of the device of Figure 4; -Figure 7 shows the device of Figure 4 with the addition of a control and check plate; and -Figure 8 is a view of the detail VIII from Figure 7.

With reference to the accompanying drawings, the numeral 1 denotes as a whole a device for breaking and closing electric circuits made in accordance with the present invention.

The device 1 disclosed is schematically illustrated in Figure 1, which also illustrates a load 2 connected to the circuit.

The device 1 generally comprises a first equipotential section 3 (which can be connected for example to a power supply voltage) and a second equipotential section 4 (which can be connected for example to the load 2) . Depending on requirements, the first and second equipotential sections 3, 4 may consist of two specific terminals which allow the device 1 to be connected to the circuit, or they may be formed by the circuit wires themselves (if the device 1 is an integral part of the circuit) The device 1 also comprises a plurality of parallel branches 5, electrically connected between the first equipotential section 3 and the second equipotential section 4. Each branch 5 in turn comprises at least one controlled switch 6 and at least one fuse 7 mounted in series with one another. In particular, Figure 1 shows a device 1 comprising five separate branches 5.

Advantageously, the fuse 7 of each branch 5 has its own tripping current (understood to be the minimum current which, after a predetermined time, causes the fuse 7 to blow and therefore the circuit to be broken) which is lower than the rated current of the breaking device 1, and higher than the rated current of the individual branch 5 (usually corresponding to the rated current of the load 2 divided by the number of branches 5) The switches 6 of the individual branches 5 are controlled in parallel so that they break and close the various branches 5 practically simultaneously.

Depending on requirements, the switches 6 may be of any type. In particular, they may consist of remote control switches or suitable electronic devices. Moreover, advantageously, each switch 6 is sized in such a way that its rated current corresponds to the rated current of the device 1 divided by the number of branches 5 present in the device 1 (increased by a safety percentage if necessary) If the switches 6 are electronic devices, each switch 6 comprises, inside it, a power transistor 8, such as a MOSFET (solution in Figure 2), an N-type channel FET, a P-type channel FET or a vertical FET.

As indicated, Figure 2 shows a device 1 made in accordance with the present invention in which

each switch 6 consists of a field-effect MOSFET.

Said device 1 is intended for use in direct current circuits.

In particular, Figure 2 schematically illustrates an electronic component called PROFET BTS555 made by Infineon Technologies AG, in which there are mounted both the power transistor 8 and an electronic circuit 9 able to measure the intensity of the current supplied through the transistor.

The component has five separate electric contacts: a first, current inlet contact 10 (which can be connected to the power supply voltage); a second and third, current outlet contact 11, 12 (which can be connected, by means of the relative fuse 7, to the load 2) , a fourth, control contact 13 (which allows activation and deactivation of the switch 6 consisting of the power transistor 8), and a fifth contact 14 on which a voltage signal can be detected proportionate to the current passing through the component. In the embodiment illustrated, the second and third contacts 11, 12 are connected to one another.

The PROFET BrS555 component is also used in the embodiment illustrated in Figures 4 to 8, where the first contact 10 consists of a metal plate, the second and third contacts 11, 12 are two pins bent downwards, and the fourth and fifth contacts 13, 14 are two pins bent upwards.

Figure 3 schematically illustrates a possible control and check circuit 15 for the device 1 in Figure 2.

The control and check circuit 15 in Figure 3 may in theory be divided into three parts: a first part 16 (the left-hand half) for controlling the switches 6, a second part 17 (the top right-hand part) for allowing detection of the presence of a blown fuse 7, and a third part 18 (on the bottom right) for supplying information about the current drawn by the load 2. Operation of the second and third parts 17, 18 is described below.

As regards operation of the first part 16 of the circuit, that is to say, the one intended for control, five identical sub-circuits 19 can be identified in it, in parallel with one another, which have a first shared terminal 20 that can be connected to a power supply voltage, a second shared terminal 21 that can be connected to earth, and a plurality of third terminals 22 (out of which the break/close command for the relative switch 6 comes) each of which can be connected to the fourth contact 13 of the relative switch 6.

In each sub-circuit 19 there is also a transistor 23 and three resistors 24.

As regards operation of the sub-circuits 19, the application of a potential difference between the first and second shared terminals 20, 21 (divided between the two resistors 24 upstream of each transistor 23) causes conduction by the various transistors 23. Consequently, an electric connection is created between the third terminals 22 and the second shared terminal 21 (and therefore with earth) . Said condition (fourth contact 13 earthed) is detected as a closing command by the power transistors 8 of the switches 6 which therefore begin conduction.

Moreover, in the control circuit 15 there is a fourth terminal 25 connected, by a plurality of diodes 26, to all of the third terminals 22, and with the function of safety block for the switches 6. Application of a positive voltage to the fourth terminal 25 is equivalent to application of a positive voltage to the third terminals 22 and so interrupts conduction by the switches 6 connected to the third terminals 22.

Advantageously, the device 1 for breaking and closing electric circuits disclosed may comprise means for evenly dividing the current in the various branches 5.

In the case described above, the dividing means consist of the controlled switches 6. In the electronic components described above any increase (reduction) in the current in a switch 6 causes an increase (reduction) in the temperature of the switch 6 and therefore an increase (reduction) in the internal resistance which, in turn, leads to a reduction (increase) in the current circulating.

In other words, a device 1 made using switches 6 of the electronic type described above is self-compensating.

In any case, in other embodiments there may be other forms of dividing (compensation) means, known or not (such as those described in patent FR 2 662 300 referred to herein) As already indicated, the device 1 disclosed may also comprise means 28 for detecting any blowing of the fuses 7 present on one of the branches 5.

In the embodiment illustrated, said detecting means 28 consist of the second part 17 of the power supply circuit described above. It comprises as many parallel paths 29 as there are branches 5 of the device 1, each having one end 30 which can be connected to the relative branch 5 in an intermediate position between the switch 6 and the fuse 7, and also having a diode 27. All of the paths 29 are also connected to a fifth, detection terminal 39 and to the second shared terminal 21 (earth) by a resistor 31.

In this way, should the switch 6 of one branch 5 develop a fault (remaining in a short circuit condition) and the relative fuse 7 trip (blow), the end 30 of the relative detecting path 29 would be at the power supply voltage which would therefore be detected on the fifth terminal 39. On the contrary, with the switches 6 open, all of the ends 30 of the paths 29 described above are earthed and so there is no signal on the fifth terminal 39.

In other embodiments there may be as many separate second parts 17 as there are paths 29, allowing more specific information about which fuse 7 has blown.

Finally, the third part 18 of the control and check circuit 15 also has a set of contacts 32 which can be connected to the fifth contacts 14 of the switches 6 described above, and a sixth terminal 33 on which a voltage proportionate to the current passing on all of the branches 5 can be detected.

As shown in Figures 4 to 8, instead of a single fuse 7, each branch 5 may be fitted with a plurality of fuses 7 in parallel. Said fuses 7 must be sized in such a way that the sum of the tripping currents of all of the fuses 7 of a single branch 5 satisfies the requirements indicated above relative to the tripping current in the case of a single fuse 7. The solution with a number of parallel fuses 7 aims to allow the use of fuses 7 with a lower rating and with faster response times.

In any case, all of the fuses 7 of a branch 5 may have the same tripping current, or the fuses 7 of a branch 5 may have different tripping currents.

The accompanying drawings show a device 1 intended for use with direct current circuits. However, breaking and closing devices 1 made in accordance with the present invention may also be used for alternating current electric circuits (with the appropriate modifications) In particular, if the device 1 is used for polyphase electric circuits (such as three-phase circuits), the device 1 substantially consists of a number of devices 1 of the type described above equal to the number of phases to be interrupted, each mounted on the relative phase.

Figures 4 to 8 illustrate a device 1 for breaking and closing electric circuits having five branches 5, each with a switch 6 of the electronic type and with two fuses 7 mounted in parallel.

In said Figures the equipotential sections 3, 4 consist of races 34 made on a supporting plate 35, to which the electric circuit wires 36 are connected.

Figures 7 and 8 also schematically illustrate a plate 37 on which the control and check circuit 15 is made, and which is connected to the pins bent upwards of the electronic switches 6, to the secondary races 38 which connect each of the switches 6 to the relative fuses 7, and, by means of a suitable wire 40, to a circuit control unit (not illustrated) In addition to what is described above, the device 1 disclosed operates as follows.

During normal operation, passing through the device 1 there is the rated current of the load I (or a lower current) divided into N branches 5.

Each branch 5 therefore has a current N equal to I/N passing through it. The branch current 5 N will advantageously be a little less than the rated current of the switches 6 mounted on the individual branches 5.

Moreover, the tripping current of the fuses 7 of the individual branches 5 will be higher than N but lower than I. The circuit will be broken and closed by means of a synchronised command given to the individual switches 6.

When, in contrast, there has been a fault which caused a switch 6 to short-circuit, at the moment when the operator gives the circuit breaking command, the switches 6 which are not faulty break the circuit.

Consequently, all of the rated current I drawn by the load 2 is forced through the branch 5 of the faulty switch 6. But as already indicated, on said branch 5 the fuse 7 (or fuses 7 as a whole) is calibrated to a tripping current lower than the rated current of the load 2, so that the fuse blows and the last branch 5 is also broken.

The fault is then detected by the suitable / 15 detecting means 28 and reported by the control unit to the operator.

At this point, depending on the calibration of the fuses 7 of the other branches 5 there are two possible alternatives: -either the sum of the tripping currents of all of the surviving fuses 7 is higher than or equal to the rated current of the load (preferred solution in many cases); in this case the load 2 can be supplied again for example to return movable parts to the home condition (e.g.: lowering the dump body of an industrial vehicle which, at the moment of the fault, was in the dump position); -or, on the contrary, the sum is lower than the rated current of the load; in this case any new breaking command would cause all of the other fuses 7 to blow and so definitively block the circuit.

Finally, the present invention also relates to an electric circuit with a power source, at least one load 2 supplied by the power source and a device 1 for breaking and closing the circuit mounted between the power source and the load 2 and made as described above.

In particular, the load 2 consists of a motor of a hydraulic power unit used in industrial vehicles, for example for tipping truck bodies or for moving arms, platforms, etc. The present invention brings important advantages.

Firstly, the use of a plurality of parallel branches with suitably calibrated switches and fuses allows safe and automatic circuit breaking even if one of the switches develops a fault.

Secondly, dividing the current in a plurality of lines allows on one hand a reduction in the stresses on the individual components, and on the other hand the use of components (switches, fuses, etc.) calibrated lower than those normally used.

Consequently, the cost is also reduced, despite the use of a larger number of components, since they are less expensive components.

It should also be noticed that the present invention is relatively easy to produce and even the cost linked to implementation of the invention is not very high.

The invention described above may be modified and adapted in several ways without thereby departing from the scope of the inventive concept.

All details of the invention may be substiLuted by other technically equivalent elements and, in practice, all of the materials used, as well as the shapes and dimensions of the various components, may be any according to requirements.

Claims

Claims 1) A device for breaking and closing electric circuits, having

its own rated operating current and characterised in that it comprises: a first equipotential section; a second equipotential section; and a plurality of parallel branches electrically connected between the first equipotential section and the second equipotential section and each having at least one controlled switch and at least one fuse mounted in series with one another; the fuse of each branch having its own tripping current which is lower than the rated current of the breaking device; and the switches of the individual branches being controlled substantially in a synchronised way.

2) The device for breaking and closing electric circuits according to claim 1, characterised in that each of the branches has a plurality of fuses mounted in parallel, the sum of the tripping currents of all of the fuses of a single branch being lower than the rated current of the device.

3) The device for breaking and closing electric circuits according to claim 2, characterised in that the fuses of a branch have the same tripping current.

4) The device for breaking and closing electric circuits according to claim 2, characterised in that the fuses of a branch have different tripping currents.

5) The device for breaking and closing electric circuits according to any of the foregoing claims, characterised in that it also comprises means for evenly dividing the current in the branches.

6) The device for breaking and closing electric circuits according to claim 5, characterised in that the means for dividing the current consist of the controlled switches.

7) The device for breaking and closing electric circuits according to any of the foregoing claims, characterised in that it also comprises means for detecting the blowing of the fuses present on one of the branches.

8) The device for breaking and closing electric circuits according to claim 7, characterised in that the detecting means comprise at least an electronic circuit operatively connected to each branch between the switch and the fuses.

9) The device for breaking and closing electric circuits according to any of the foregoing claims, characterised in that it is a device for direct current circuits.

10) The device for breaking and closing electric circuits according to any of the claims from 1 to 8, characterised in that it is a device for single-phase alternating current circuits.

11) The device for breaking and closing electric circuits according to any of the claims from 1 to 8, characterised in that it is a device for polyphase alternating current circuits, and it comprises the equipotential sections and the branches in parallel for each phase of the circuit for which they are intended.

12) The device for breaking and closing electric circuits according to any of the foregoing claims, characterised in that the switches are remote control switches.

13) The device for breaking and closing electric circuits according to any of the claims from 1 to 11, characterised in that the switches are electronic devices.

14) The device for breaking and closing electric circuits according to claim 13, characterised in that each of the electronic devices comprises, inside it, a power transistor.

15) The device for breaking and closing electric circuits according to claim 14, characterised in that the power transistor is a MOSFET.

16) The device for breaking and closing electric circuits according to claim 14, characterised in that the power transistor is an N-type channel FET.

17) The device for breaking and closing electric circuits according to claim 14, characterised in that the power transistor is a P-type channel FET.

18) The device for breaking and closing electric circuits according to claim 14, characterised in that the power transistor is a vertical FET.

19) The device for breaking and closing electric circuits according to any of the foregoing claims, characterised in that the branches are all identical.

20) An electric circuit having a power source, at least one load supplied by the power source and a device for breaking and closing the circuit mounted between the power source and the load, characterised in that the device for breaking and closing the circuit is made according to any of the foregoing claims.

21) The electric circuit according to claim 20, characterised in that the load consists of an electric motor.