| JP3500232 | HOT WATER SUPPLY SYSTEM |
| JPH1089681 | PRESSURE SPRAY TYPE COMBUSTION EQUIPMENT |
BERTELLI PIERLUIGI (IT)
| US5085574A | 1992-02-04 | |||
| US4865538A | 1989-09-12 | |||
| US5917691A | 1999-06-29 |
| CLAIMS
1. A control device (1) for a safety element of an electrical appliance for domestic use or for a gas appliance, comprising an electronic circuit (1) which receives, for controlling said safety element, an electrical signal (V) generated by a control unit (100), said element being a gas valve or other electrical component requiring safety control, characterised by comprising a static switch (9) functionally cooperating with a capacitor (16) which itself cooperates with said safety element, the frequency piloting of the static switch (9) by said control signal (V) enabling controlled discharge of the capacitor (16) and the activation of said element, a possible interruption in the electrical power supply to the static switch (9) or a generic fault in the device leading to the deactivation of the controlled safety element.
2. A device as claimed in claim 1 , characterised in that the capacitor (16) cooperates with the safety element via a relay (6) arranged to control a change- over switch (5) operating across fixed contacts (27) of an electrical supply line to the safety element, the capacitor (16) discharging across said relay (6) as a result of piloting of the static switch (9) such as to maintain said change-over switch (5) closed across said fixed contacts (27) to power the safety element.
3. A device as claimed in claim 1 , characterised in that the capacitor (16) is directly connected to the safety element, this latter comprising an electrical actuator powered by the device and receiving the discharge of the capacitor, subsequent to which said actuator becomes activated.
4. A device as claimed in claim 1 , characterised in that the control signal (V) is a square wave signal. 5. A device as claimed in claim 1, characterised in that the control unit (100) for generating said control signal (V) is preferably of microprocessor type, said unit (100) governing the operation of other electrical components of the electrical appliance.
6. A device as claimed in claim 1 , characterised in that the static switch (9) is connected to a reference voltage and to a circuit branch (10) connected to a predetermined positive d.c. voltage (+VCC), to said branch (10) there being connected at least one further static switch (11) to which an electrical branch (15) is connected comprising said capacitor (16), this latter also being connected to a further circuit branch (17) in which a diode (18) is present.
7. A device as claimed in claim 6, characterised in that the further circuit branch and the relay are connected to the reference voltage.
8. A device as claimed in claim 6, characterised in that the further circuit branch is connected to the positive d.c. voltage (+VCC), the control signal present in said branch being complementary to that present in this latter when this is connected to the reference voltage.
9. A device as claimed in claim 6, characterised in that the electrical branch (15) comprising the capacitor (16) is present downstream of the further static switch (11) and upstream of another static switch (12).
10. A device as claimed in claim 6, characterised in that the electrical branch (11) comprising the capacitor (16) is present downstream of the static switch (11) and upstream of a diode (30).
11. A device as claimed in claim 2, characterised in that the relay (6) is of the type operating on different contact types, such as a single pole, double pole, switching or change-over contact.
12. A device as claimed in claim 1 , characterised in that the control signal (V) is applied to the electronic circuit (1) via a filtering network positioned in the input branch (2). 13. A device as claimed in claim 12, characterised in that the filter consists of an R-C filter connected in series with the input branch.
14. A method for piloting a control device for a safety element of an electrical appliance for domestic use such as a washing machine, wash-drier, dishwasher, oven or similar household electrical appliance or a gas appliance, said device being obtained in accordance with claim 1 and comprising a static switch (9) functionally cooperating with a capacitor (16) connected to the safety element, said method being characterised in that the device piloting comprises the following steps: a) generating a voltage pulse of predefined (long) duration and fed to the transistor 9 to completely charge the capacitor 16; b) generating a subsequent predefined-duration voltage pulse of opposite value to that generated in step a), in order to activate the safety element controlled by a full voltage pulse; c) frequency controlling (2) the transistor (9) in order to maintain the controlled safety element active at a voltage lower than the activation voltage. |
CONTROL DEVICE FOR A SAFETY ELEMENT OF A DOMESTIC ELECTRICAL APPLIANCE OR OF A GAS APPLIANCE
The present invention relates to a control circuit for a safety element of an electrical appliance for domestic use (for example a washing machine, a dishwasher, an oven or the like) or of a gas appliance in accordance with the introduction to the main claim.
With particular but non-limiting reference to a gas appliance, it is known that the gas shutoff valve is powered via electrical control relays while undergoing safety control which ensures that it closes in the case of malfunction or absence of electrical power. The conventional systems and current European regulations accept as a necessary and sufficient condition for gas appliance safety that the gas valve or gas shutoff valve be powered via a circuit arrangement in series with two independent elements or switches. These latter are usually powered at line voltage.
This circuit arrangement is considered safe, with short-circuiting of the contacts across which said switches close being excluded a priori as a fault mode. This is with the proviso that the relays exceed a minimum number of switchings at rated load and that they are protected by an adequate fuse. In addition, mechanical valve faults are also excluded a priori, because the valve is subjected to a life test involving a very large number of manoeuvres during which it must not undergo any damage.
An object of the present invention is to provide a control device for a safety member, such as the said gas valve, which represents an improvement over known devices.
A particular object of the invention is to provide a device of the stated type which enables the safety level of the electrical control applied to the controlled element to be increased.
These and other objects which will be apparent to the expert of the art are attained by a device in accordance with the accompanying claims. The present invention will be more apparent from the accompanying drawings, which are provided by way of non-limiting example and in which: Figure 1 is a circuit diagram of a first embodiment of a device according to the invention;
Figure 2 shows a diagram similar to that of Figure 1 , but of a second embodiment of the device of the invention; Figure 3 shows a circuit diagram similar to that of Figure 1 , but of a third embodiment of the device of the invention; and
Figure 4 shows a diagram similar to that of Figure 1 , but of a fourth embodiment of the device of the invention.
With reference to said figures, similar elements are indicated by the same reference numerals therein. With reference to Figure 1 , a device according to the invention presents a circuit configuration indicated overall by 1. This configuration presents an input branch 2 connected to a known control unit 100 such as a microprocessor circuit, arranged to control the correct operation of the appliance on which said device is mounted (for example a gas appliance). This unit generates a square wave control signal V of suitable frequency and duty cycle, chosen for example as a function of the utilized values of the components of the circuit configuration 1 and on the basis of the safety criteria required by current regulations; this signal controls the opening and closure of a change-over switch 5. In particular, this signal V is used to control a relay 6 to which the conductor 5 is connected.
More particularly, the signal V present in the input branch 2 is fed to the base of a static switch 9, of which the emitter is connected to earth and the collector is connected to a branch 10 to which are connected the bases of two further static
switches or transistors 11 , 12 connected together in parallel. A resistor 13 is connected to a point on the branch 10 at a fixed positive d.c. voltage (for example 24V d.c.) and has its other end connected to the collector of the transistor 11. The emitter of this latter is connected to the collector of the other transistor 12, between the two there being connected a branch 15 containing a capacitor 16 connected to a circuit branch 17 containing a diode 18 and to the relay 6. These latter and the transistor 12 are then connected to a reference signal (for example earth or another predetermined voltage value). The switch 5 (single pole switch, double pole switch, change-over switch or the like) is arranged to close across fixed contacts 27 of a power supply line to an electrical safety component of the gas appliance, such as a gas shutoff valve or similar device.
It will now be assumed that the device of Figure 1 is to be used. At commencement, the transistor is maintained closed (rest condition) by usual piloting effected by the unit 100.
The transistor 9 is then opened for the time necessary and sufficient to completely charge the capacitor 16 via the transistor 11 and the diode 18. The activation sequence for the circuit 1 can consist of the following steps: a) generating a pulse of predefined (long) duration in the branch 2 for the purpose of closing the transistor 9 and completely charging the capacitor 16; b) generating a predefined-duration pulse opposing that generated in step a), in order to activate the relay 6 with a full voltage pulse; c) frequency controlling the transistor 9 in order to maintain the controlled element (relay 6) active at a voltage lower than the activation voltage. The transistor 9 is then again activated in order to transfer the capacitor charge as an energizing pulse across the coil of the relay 6 via the transistor 12. When sensed that the switch 5 has switched over, it is maintained closed by the frequency control of the transistor 9 such as to enable cyclic recharge (short OFF time of transistor 9) and transfer
of the charge stored in the relay 6 in the aforestated manner (long ON time of transistor 9).
If a fault in the device 1 or a possible problem in piloting the transistor 9 or a fault in one or more of the components arises, the relay 6 is de-energized permanently and the change-over switch 5 remains in the open position, i.e. in a safety position for the component powered via its closure across the fixed contacts 27.
The variant of Figure 2 is very similar to the embodiment of Figure 1 ; however in Figure 2 the device 1 is connected to reverse polarity power supply lines (the branch 17 and the relay 6 are connected to the positive voltage). The operation of the device 1 is nevertheless similar to that of Figure 1. The control signal V is characterised by having a wave shape complementary to that of the signal V used in the circuit configuration of Figure 1. This characteristic is important to satisfy regulations and for final product safety as required by current standards, e.g. EN60730, EN60335.
The embodiments of the invention shown in Figures 3 and 4 are similar to those of Figures 1 and 2 respectively, but with the transistor 12 being replaced by a diode 30. In Figures 2 and 4, by way of non-limiting example a change-over switch 5 is shown of the type operating on two pairs of fixed contacts positioned in power supply lines of two electrical components of the circuit configuration 1. This is applicable for example where the standard specifies two-pole disconnection or where it is useful or necessary for the purposes of the application. The invention offers a control device for an electrical safety component of an appliance for domestic use or a gas appliance, such as a gas valve, which presents an adequate intervention rate and which ensures that this element assumes a safety position both when required in the case of correct control device operation (to achieve a correct control sequence by the unit 100), and in
the case of control device malfunction or fault.
Various variants of the invention have been described. Others are however possible in the light of the aforegoing description (such as one in which the inventive device is applied to another electrical appliance such as a household electrical appliance), these being considered as falling within the scope of the following claims.
A preferred embodiment of the invention has been described in which the safety element is controlled by a device in which a change-over switch 5 is piloted to close fixed contacts 27 of a power supply line for that element. However, in a different embodiment, the inventive device comprises the safety element itself (for example a gas valve provided with an electrical actuator acting on a movable valving element in a gas conduit) but connected to the capacitor 16. In other words, the invention can also comprise said element (or rather its electrical actuator) directly connected to the capacitor and physically positioned in place of the relay 6 within the circuit configuration 1 of one of the Figures from 1 to 4.
The control signal V can be applied to the electrical circuit 1 directly (as in the figures), or via a filtering relay connected into the input branch 2 to make the circuit operation more selective on the basis of the frequencies and wave form of the control signal V.
By way of non-limiting example, the filter network can consist of an R-C filter connected in series with the input branch.