TEXT OF THE DESCRIPTION

Field of the invention

The present invention relates to a door locking device for domestic appliances, in particular for washing machines .

A door locking device has the purpose of ensuring that the door of the domestic appliance is locked in the closed position and can only be opened when a sufficient time has elapsed after the ending of an operating cycle.

Background of the invention

EP-A-1137030 discloses a door locking device according to the preamble of claim 1, having an electric switching unit which includes a bimetal strip connected to a PTC resistor and a bistable switching device electrically connected to the bimetal strip through the PTC resistor and including a locking pin which in an energized position of the bistable switching device engages and locks a retaining slider which locks the door in the closed position.

In some cases, in addition to the locking function, also a door sensing switch is requested. The door sensing switch is indirectly actuated by the door of the domestic appliance. The purpose of the additional door sensing switch is to prevent the start of the domestic appliance (e.g. the start of a washing cycle) when the door is open and in some special circumstances which are described in one of the IEC standards for domestic appliances.

Object and summary of the invention

The object of the present invention is to provide a door locking device with an integrated door sensing switch capable of sensing the closed condition of the door in a de-energized condition of the door locking device, which requires little space and can be added with only small modifications also to existing versions of door locking devices .

In accordance with the present invention, this object is achieved by a door locking device having the features of claim 1.

Preferred embodiments of the inventions are disclosed in the dependent claims.

Brief description of the drawings

The present invention will now be described in detail with reference to the annexed drawings, given purely by way of non-limiting example, in which:

- figure 1 is a perspective view of a door locking device according to the present invention,

- figure 2 is a perspective cross-section taken along the line II-II of figure 1,

- figures 3 and 4 are schematic cross-sections showing the door locking device according to the present invention respectively in the open door condition and in the closed door condition, and

- figures 5 and 6 are partial perspective views showing the operation of the door sensing switch according to the present invention.

Detailed description of embodiments of the invention With reference to the drawings, a door locking device according to the present invention is indicated by the reference number 10. The door locking device 10 comprises a housing 12 carrying at least two and preferably three fixed electric contacts indicated respectively N, L and C. The fixed electric contacts N, L, C include respective metal blades which project from a lateral wall of the housing 12. The door locking device 10 comprises a retaining slider 14 which is movable with respect to the housing 12 in a direction indicated by the arrow A. The retaining slider 14 has an opening 16 for receiving a hook 18 connected to the door of a domestic appliance, such as a washing machine. The retaining slider 14 is movable with respect to the housing 12 in the direction A between a rest position corresponding to the open position of the door and a locking position corresponding to the closed position of the door.

With reference to figures 3 and 4, a helical compression spring 20 is set between the retaining slider 14 and a mounting plate 22. The retaining slider 14 is movable in a space defined between a bottom wall 24 of the housing 12 and the mounting plate 22. The spring 20 biases the retaining slider 14 towards its rest position shown in figure 3. When the door of the domestic appliance is closed, the hook 18 connected to the door enters into the opening 16 of the retaining slider 14 and moves the retaining slider 14 in the locking position shown in figure 4. The slider 14 can move from the rest position to the locked position in both directions depending on the model of door lock. In the position of figure 4 the retaining slider 14 locks the hook 18 and prevents opening of the door .

With reference to figures 3 and 4, the door locking device 10 comprises an electric actuator 26 housed into the housing 12. In the embodiment shown in the drawings the electric actuator 26 comprises a bistable switching device 28 electrically connected to the second electric contact L. The bistable switching device 28 is made up of a strip spring 30 and a hoop spring 32. The strip spring 30 and hoop spring 32 are preferably made of a single metal strip and have a common end fastened to a metal strip 34 connected to or integral with the second electric terminal L. The strip spring 30 and hoop spring 32 are elastically joined by a coupling spring 36. Depending on the position of the strip spring 30, the hoop spring 32 of the bistable switching device 28 jumps over from a de-energized stable position shown in figure 3 to an energized stable position shown in figure 4.

The bistable switching device 28 includes a locking pin 38 connected to the free end of the hoop spring 32. The free end of the locking pin 38 extends through a hole 40 of the bottom wall 24. The locking pin 38 is intended to engage a locking hole 42 of the retaining slider 14 when the retaining slider 14 is in the locking position and when the bistable switching device 28 is in the energized stable position (see figure 4).

The hoop spring 32 is provided with a movable contact 44 close to the free end. In the energized position of the bistable switching device 28 the movable contact 44 abuts against a fixed contact 46 carried by the third electric contact C.

The electric actuator 26 also comprises a bimetal strip 48, a compensating bimetal strip 50 and a PTC resistor 52. The PTC resistor 52 is electrically connected between the bimetal strip 48 and the strip spring 30. A first end of the bimetal strip 48 is leaned against an adjusting screw 54 and the second end thereof is leaned against the compensating bimetal strip 50. Both ends of the compensating bimetal strip 50 are leaned against the bottom wall 54 of the housing 12. The adjusting screw 54 is screwed into a threaded hole of an intermediate contact 56 which is leaned against the bottom wall 24. The head of the adjusting screw 54 is accessible through a hole of the bottom wall 24.

In alternative, the electric actuator 26 might include an electromagnet, or other types of electric actuators, for moving the locking pin 38 between the unlocked position and the locked position.

The door locking device 10 comprises an integrated door sensing switch 58 electrically connected between the first electric contact N and the electric actuator 26.

With reference to figures 5 and 6, the door sensing switch 58 includes an helical compression spring 62 made of electrically conducting material and a spring holder 60 preferably made of plastic material. The helical compression spring 62 has a first end which abuts against a lateral projection 64 of the first electric contact N. The spring holder 60 has a seat 63 for the helical compression spring 62. The seat 63 has an open end 65 (figure 5) through which a second end of the helical compression spring 62 is exposed.

The spring holder 60 is movable between a disconnected circuit position shown in figure 5 and a connected circuit position shown in figure 6. The compression spring 62 elastically biases the spring holder 60 towards the connected circuit position, in which the spring holder 60 abuts against the intermediate contact 56.

As shown in figure 5, in the disconnected circuit position the spring holder 60 is separated from the intermediate contact 56. In this condition, the second end of the spring 62 is separated from the intermediate contact 56 and the electric connection between the first electric contact N and the intermediate contact 56 is interrupted. In the connected circuit position shown in figure 6 the spring holder 60 abuts against the intermediate contact 56. In this condition, the second end of the spring 62 is in contact with the intermediate contact 56. Therefore, there is an electric connection between the first electric contact N and the intermediate contact 56 through the spring 62. In this condition, the bimetal strip 48 is electrically connected to the first electric contact N through adjusting screw 54, intermediate contact 56, spring 62 and lateral projection 64.

The spring holder 60 has a projection 66 which extends through an aperture of the bottom wall 24 and cooperates with a ramp portion 68 of the retaining slider 14. As best shown in figures 5 and 6, the ramp portion 68 has a raised portion 70 and a recessed portion 72. When the retaining slider 14 is in the rest position, corresponding to the open condition of the door, the projection 66 abuts against the raised portion 70 of the ramp portion 68 as shown in figures 3 and 5. In this condition the spring holder 60 is in the disconnected circuit position and, as described above, the electric connection between the first electric contact N and the bimetal strip 48 is interrupted.

When the retaining slider 14 is in the locked position corresponding to the closed condition of the door, the projection 66 is situated in correspondence with the recessed portion 72 of the ramp 68. In this condition, the spring holder 60 is biased by the spring 62 in the connected circuit position. In this condition, the spring 62 closes the electric connection between the first electric contact N and the bimetal strip 48.

When the door sensing switch 58 is in the open condition, electric current cannot flow through the bimetal strip 48 and the PTC resistor 52. Accordingly, the bistable switching device 28 is in the de-energized position shown in figure 3. In this position the locking pin 38 is raised and the retaining slider 14 is unlocked and free to move in the direction A.

When the retaining slider 14 is moved in the locking position by the hook 18, the door sensing switch 58 moves to the closed position and closes the circuit between the first electric contact N and the bimetal strip 48. In this condition, when voltage is applied between the electric terminals N and L, electric current flows from the first electric contact N to the second electric contact L through the door sensing switch 58, the intermediate contact 56, the adjusting screw 54, the bimetal strip 48, the PTC resistor 52 and the strip spring 30. The PTC resistor warms up and the bimetal strip 48, which is in touch with the PTC resistor 52, gets warm too and pushes the PTC resistor 52 towards the strip spring 30. When the strip spring 30 undergoes a certain displacement, the hoop spring 32 jumps over into the energized position shown in figure 4. In this condition, the locking pin 38 moves to the locking position and engages the locking hole 42 of the retaining slider 14, thereby locking the retaining slider 14 in the locking position. At the same time, the contacts 44, 46 enter into mutual contact and connect electrically the second electric contact L with the third electric contact C, thereby confirming that the door is locked.