Door lock device with thermal protection and method for thermal protection of a door lock device in a household appliance

Abstract

 A door lock device includes an electrically actuatable locking mechanism (10), provided with actuation coils (10a), and a driving device (11), coupled to the actuation coils (10a) for delivering driving pulses (I) in response to commands of a user. The door lock device is equipped with a logic control unit (12), configured to determine an estimated temperature (T_C, T_I) of the electric actuation means (10a) and to prevent delivery of driving pulses (I) by the driving device (11), if the estimated temperature (T_C, T_I) is expected to rise above a safety temperature threshold (T_TH1, T_TH2) as a consequence of delivering a driving pulse (I).

Description

[0001] The present invention relates to a door lock device with thermal protection and to a method for thermal protection of a door lock device in a household appliance.

[0002] It is known that several household appliances, such as washers, are equipped with safety door lock devices to prevent operation of the appliance when the door is not properly locked.

[0003] Two kinds of door lock devices are currently available.

[0004] Delayed door lock devices enable opening the door of the appliance only after a time interval has elapsed since a washing cycle has been completed or paused in a condition wherein opening the door is allowed (e.g. there is no water in the washing compartment). Delayed door lock devices are based on use of thermosensitive components (normally PTC thermistors coupled to bimetallic deformable components). In use, PTC thermistors are energized by supplying a current and rapidly increase their temperature, causing deformation of bimetal components. A locking mechanism is thus actuated to a closing position, as long as the PTC thermistors are energized. When power supply is removed, PTC thermistors cool down and the bimetal components switch to a rest configuration in which the locking mechanism is released.

[0005] A drawback of delayed door lock devices resides in that a current must be supplied to the PTC thermistors during a whole washing cycle. Therefore, power consumption is quite high. Moreover, users must every time wait for a while before being allowed to open the door, until the PTC thermistors cool and the locking mechanism is released.

[0006] Instant door lock devices are operated by current pulses that are supplied by a power source in response to commands of a user. Subsequent pulses alternately lock and release door lock devices. A control button is normally available to this end. Instant door lock devices do not require continuous power supply during washing cycles and, as a rule, may be immediately operated at any time, provided that cycle progress so allows. However, temperature of door lock devices may dramatically increase following upon repeated current pulses and some thermal protection is required to prevent overheating. Thus, additional circuits must be provided to forbid release of current pulses when temperature of locking devices exceeds a safety range. Also thermal protection circuits include thermosensitive components and may be based on PTC thermistors. Anyway, additional costs are incurred and overall risk of component failure is increased.

[0007] The object of the present invention is to provide a door lock device with thermal protection and a method for thermal protection of a door lock device that are free from the above described drawbacks.

[0008] According to the present invention, a door lock device and a method for thermal protection of a door lock device are provided, as claimed in claims 1 and 10, respectively.

[0009] For the understanding of the present invention, some embodiments thereof will be now described, purely as non-limitative examples, with reference to the enclosed drawings, wherein:

• figure 1 is simplified perspective view of a household appliance;
• figure 2 is a simplified block diagram of a door lock device according to one embodiment of the present invention and incorporated in the household appliance of figure 1;
• figure 3 is a flowchart relating to a first procedure carried out in the door lock device of figure 2; and
• figure 4 is a flowchart relating to a second procedure carried out in the door lock device of figure 2.

[0010] In figure 1, a household appliance, that in the embodiment herein described is a washer, is generally designated by the reference numeral 1.

[0011] The appliance 1 comprises a body 2, a washing compartment 3, a power supply unit 4, both accommodated in the body 2, and a door 5, for providing access to the washing compartment 3. In the embodiment herein described, the washing compartment 3 is a rotary basket and the door is arranged on a front panel 2a of the body 2.

[0012] The door 5 is equipped with an instant-type door lock device 7 to prevent operation of the appliance 1 when the door 5 is not properly locked.

[0013] As illustrated in figure 2, the door lock device 7 comprises a locking mechanism 10, a driving device 11 and a logic control unit 12.

[0014] The locking mechanism 10 is electrically actuatable by current pulses I to alternately lock and unlock the door 5. The locking mechanism 10 maintains its current configuration, either locked or unlocked, until another current pulse I is received.

[0015] The driving device 11 is supplied by the power supply unit 4 and is moreover coupled to the locking mechanism 10 to deliver current pulses I, thereby causing the locking mechanism 10 to alternately lock and unlock. Current pulses I are released by the driving device 11 in response to driving signals S_D provided by the logic control unit 12, as explained hereinafter.

[0016] The logic control unit 12 comprises a main module 15, a temperature estimation module 16, a test module 17 and a state storage element 18.

[0017] Moreover, the logic control unit 12 is coupled to a control button 20, provided on the front panel 2a of the body 2 and operable by a user to produce lock/unlock signals S_LU for the logic control unit 12 (see also figure 1).

[0018] The main module 15 controls operation of the whole appliance 1 and, in particular, determines progress of a washing cycle according to a program selected by a user. Among other functions, the main module 15 generates a consent signal S_C to enable opening the door 5 when progress of the washing cycle so allows.

[0019] The temperature estimation module 16 determines and cyclically updates estimated values of an operative temperature T of actuating coils 10a of the locking mechanism 10, which run a risk of overheating if several current pulses are supplied in a short time. Currently estimated values T_C of the operative temperature T are supplied to the test module 17.

[0020] The state storage element 18 stores a state logic signal ST that is indicative of a current state of the locking mechanism 10. Namely, the state logic signal ST has a first logic value when the locking mechanism 10 is locked and a second logic value when the locking mechanism 10 is unlocked. The state logic value is updated every time the locking mechanism 10 is operated.

[0021] Based on the consent signal S_C, on a currently estimated value T_C of the operative temperature T and on the state logic value ST, the test module 17 determines whether or not a current pulse I is to be delivered to the actuating coils 10a of the locking mechanism 10 in response to lock/unlock signals S_LU that are generated when the control button 20 is operated by a user.

[0022] In one embodiment, determination is made by the test module 17 in accordance to a procedure illustrated in figure 3.

[0023] The procedure is activated upon operation of the control button 20 by the user.

[0024] In a first step (block 100), the test module 17 receives the consent signal S_C from the main module 15, the state logic signal ST from the state storage element 18 and the currently estimated value T_C of the operative temperature T from the temperature estimation module 16.

[0025] The consent signal S_C is first tested to check consent of the main module 15 to pulse generation (block 110). If consent is denied (block 110, output NO), the procedure is terminated (block 120). Otherwise (block 110, output YES), the state logic signal ST is tested to identify the current state of the locking mechanism 10 (block 130).

[0026] If the locking mechanism 10 is found to be locked (block 130, output YES), an incremented temperature value T_I is compared to a first safety temperature threshold T_TH1 (test condition: T_I < T_TH1; block 140). The incremented temperature value T_I is an estimation of the operative temperature T that is expected as a consequence of delivering another current pulse I. The incremented temperature value T_I is calculated by adding an expected temperature increment ΔT, associated with delivery of a current pulse I, to the currently estimated value T_C of the operative temperature T. In the embodiment herein described, the expected temperature increment ΔT is a constant, independent of the currently estimated value T_C of the operative temperature T. The incremented temperature value T_I is calculated in advance to possibly delivering a current pulse I.

[0027] In practice, the following condition is tested in block 140:

[0028] If the incremented temperature value T_I is lower than the first safety temperature threshold T_TH1 (block 140, output YES), a driving signal S_D is sent to the driving device 11 to trigger a current pulse I and actuate the locking mechanism 10 (block 150). The driving signal S_D is also provided to the temperature estimation module 16, for the purpose of updating the currently estimated value T_C, and to the state storage element 18, that switches the state logic signal ST between its first and second logic values. Otherwise (block 140, output YES), the procedure is terminated (block 120), thereby preventing delivery of current pulses I by the driving device 11, because the incremented temperature value T_I exceeds a safety range and the actuation coils 10a of the locking mechanism 10 may be subjected to overheating.

[0029] If the locking mechanism 10 is found to be unlocked on testing the state logic signal ST (block 130, output NO), the incremented temperature value T_I is calculated and compared to a second safety temperature threshold T_TH2 (test condition: T_I < T_TH2; block 160). In the embodiment herein described, the second safety temperature threshold T_TH2 is lower than the first safety temperature threshold T_TH1. In the present embodiment, in particular, the second safety temperature threshold T_TH2 is equal to T_TH1 - ΔT, so that in practice in block 160 the following condition is tested:

[0030] Anyway, another value could be used for the second safety temperature threshold T_TH2.

[0031] If the incremented temperature value T_I is lower than the second safety temperature threshold T_TH2 (block 160, output YES), the locking mechanism 10 is actuated by sending a driving signal S_D to the driving device 11, to trigger a current pulse I (block 150). Otherwise (block 140, output YES), the procedure is terminated (block 120).

[0032] According to the above described procedure, in practice, the driving device 11 delivers current pulses I in response to commands imparted by a user through the control button 20, unless generation of current pulses I is inhibited by the logic control unit 12, in order to prevent overheating of the actuating coils 10a of the locking mechanism 10.

[0033] Different safety temperature thresholds are used to enable switching of the locking mechanism 10 from the locked state to the unlocked state and from the unlocked state to the locked state. In particular, a current pulse to lock the door 5 through the locking mechanism 10 is permitted only in case another current pulse I can be soon after delivered to unlock the door 5 without exceeding the highest temperature safety threshold (i.e. the first temperature safety threshold T_TH1). Thus, the door lock device 7 is always in condition to respond without any delay to a request to unlock the door 5.

[0034] In another embodiment, however, the incremented temperature value T_I is compared to a single safety temperature threshold, irrespective of the locked or unlocked state of the locking mechanism 10. In this case, the state storage element 18 is not required.

[0035] The estimation of the operative temperature T is determined and updated by the temperature estimation module 16 according to the procedure illustrated in figure 4.

[0036] A minimum temperature value T_MIN is selected as the currently estimated value T_C of the operative temperature T during an initialization step (block 200). In the embodiment herein described, the minimum temperature value T_MIN is the highest temperature value that may be reached in the working environment of the locking mechanism 10 during a washing cycle. Hence, the minimum temperature value T_MIN is the highest temperature that the actuating coils 10a of the locking mechanism 10 may reach in case no current pulses I are sent by the driving device 11. Risk of underestimating the operative temperature T is thus avoided. In the present embodiment, the minimum temperature value T_MIN is 60°C.

[0037] Then, generation of a current pulse I is tested (block 210). To this end, the temperature estimation module 16 is coupled to the test module 17 for receiving the driving signal S_D. Thus, actual production of current pulses I is tested.

[0038] If, based on the driving signal S_D, generation of a current pulse I is recognized (block 210, output YES), the currently estimated value T_C of the operative temperature T is increased by the expected temperature increment ΔT (block 220). Then, a new test for generation of current pulses I is carried out (block 210). Otherwise (block 210, output NO), the currently estimated value T_C is decremented according to a cooling law (block 230). In the embodiment herein described, decrement is determined according to a first order exponential cooling law, namely:


wherein T₀ is the most recent peak value of the currently estimated value of the operative temperature, t is time elapsed from the most recent peak value and τ is a calibratable time constant. Next, a new test for generation of current pulses I is carried out (block 210).

[0039] The door lock device 7 provides for extremely simple, yet effective thermal protection of actuating coils 10a of the locking mechanism 10, without any need of additional components. Most of modern household appliances already include a logic control unit to control available functions. Thus, the existing logic control unit may be configured to carry out required test and temperature updating procedures as described above.

[0040] Finally, it is clear that numerous modifications and variations may be made to the method and device described and illustrated herein, all falling within the scope of the invention, as defined in the attached claims.

[0041] In particular, estimated values of the operative temperature may be updated according to different procedures. For example, effect of current pulses may be accounted for by variable temperature increments as a function of currently estimated temperature. Also cooling may be determined according to different cooling laws.

[0042] Other temperature thresholds than those described may be used, according to the need.

Claims

1. Door lock device comprising:

an electrically actuatable locking mechanism (10), provided with electric actuation means (10a);

a driving device (11), coupled to the electric actuation means (10a) for delivering driving pulses (I) in response to commands of a user;

characterized by a logic control unit (12), configured to determine an estimated temperature (T_C, T_I) of the electric actuation means (10a) and to prevent delivery of driving pulses (I) by the driving device (11), if the estimated temperature (T_C, T_I) is expected to rise above a safety temperature threshold (T_TH1, T_TH2) as a consequence of delivering a driving pulse (I).

2. Door lock device according to claim 1, wherein the logic control unit (12) is further configured to determine a currently estimated temperature value (T_C) and an incremented estimated temperature value (T_I) that is expected in response to delivering a driving pulse (I), starting from the currently estimated temperature value (T_C) .

3. Door lock device according to claim 2, wherein the logic control unit (12) is further configured to determine the incremented estimated temperature value (T_I) by adding an expected temperature increment (ΔT) to the currently estimated temperature value (T_C).

4. Door lock device according to claim 2 or 3, wherein the logic control unit (12) comprises a test module (17) configured to compare the incremented estimated temperature values (T_I) with the safety temperature threshold (T_TH1, T_TH2).

5. Door lock device according to claim 4, wherein the test module (17) is further configured to generate a driving signal (S_D) for the driving device (11) to trigger delivery of a driving pulse (I) if the incremented estimated temperature values (T_I) is lower than the safety temperature threshold (T_TH1, T_TH2) and to prevent delivery of a driving pulse (I) if the incremented estimated temperature values (T_I) is greater than the safety temperature threshold (T_TH1, T_TH2).

6. Door lock device according to claim 4 or 5, wherein the logic control unit (12) comprises a state storage element (18) for storing a logic signal (ST) indicative of selectively one of a locked state and an unlocked state of the locking mechanism (10), and wherein the test module (17) is further configured receive the logic signal (ST) and to compare the incremented estimated temperature values (T_I) with a first safety temperature threshold (T_TH1), when the logic signal (ST) is indicative of the locked state of the locking mechanism (10), and with a second safety temperature threshold (T_TH2), lower than the first safety temperature threshold (T_TH1) , when the logic signal (ST) is indicative of the unlocked state of the locking mechanism (10).

7. Door lock device according to any one of claims 2 to 6, wherein the logic control unit (12) comprises a temperature estimation module (16) configured to update the currently estimated temperature value (T_C) based on a first order exponential law, in the absence of delivered driving pulses (I).

8. Door lock device according to claim 7 as appended to claim 3, wherein the temperature estimation module (16) is configured to update the currently estimated temperature value (T_C) by adding the expected temperature increment (ΔT) to the currently estimated temperature value (T_C) in response to recognition of delivery of a driving pulse (I).

9. Household appliance comprising a door and a door locking device (7) according to any one of the foregoing claims, for selectively locking and unlocking the door (5).

10. Method for thermal protection of a door lock device comprising:

electrically actuating a locking mechanism (10) of a door lock device (7), by delivering driving pulses (I) to an electric actuation means (10a) thereof, in response to commands of a user;

characterized by:

determining an estimated temperature (T_C, T_I) of the electric actuation means (10a); and

preventing delivery of driving pulses (I) by the driving device (11), if the estimated temperature (T_C, T_I) is expected to rise above a safety temperature threshold (T_TH1, T_TH2) as a consequence of delivering a driving pulse (I).

11. Method according to claim 10, wherein determining the estimated temperature (T_C, T_I) comprises determining a currently estimated temperature value (T_C) and an incremented estimated temperature value (T_I) that is expected in response to delivering a driving pulse (I), starting from the currently estimated temperature value (T_C) .

12. Method according to claim 11, wherein determining the incremented estimated temperature value (T_I) comprises adding an expected temperature increment (ΔT) to the currently estimated temperature value (T_C).

13. Method according to claim 11 or 12, comprising:

comparing the incremented estimated temperature values (T_I) with the safety temperature threshold (T_TH1, T_TH2) ;

triggering delivery of a driving pulse (I) if the incremented estimated temperature values (T_I) is lower than the safety temperature threshold (T_TH1, T_TH2) ; and

preventing delivery of a driving pulse (I) if the incremented estimated temperature values (T_I) is greater than the safety temperature threshold (T_TH1, T_TH2) .

14. Method according to claim 13, wherein comparing comprises:

identifying a current state of the locking mechanism (10) between a locked state and an unlocked state;

comparing the incremented estimated temperature values (T_I) with a first safety temperature threshold (T_TH1), when the current state of the locking mechanism (10) is the locked state of the locking mechanism (10); and

comparing the incremented estimated temperature values (T_I) with a second safety temperature threshold (T_TH2), lower than the first safety temperature threshold (T_TH1), when the logic signal (ST) is indicative of the locked state of the locking mechanism (10).

15. Method according to any one of claims 11 to 14, wherein determining the estimated temperature (T_C, T_I) comprises updating the currently estimated temperature value (T_C) based on a first order exponential law, in the absence of delivered driving pulses (I).

16. Method according to claim 15 as appended to claim 12, wherein determining the estimated temperature (T_C, T_I) comprises updating the currently estimated temperature value (T_C) by adding the expected temperature increment (ΔT) to the currently estimated temperature value (T_C) in response to recognition of delivery of a driving pulse (I).

Drawing