The invention lies in the field of extractor hoods. Such extractor hoods are used on a large scale in houses or other accommodation having a ventilation system, wherein a fan which is placed centrally and at least at a distance from suction openings can draw off air, vapour etc. from a space for ventilating.

Such an extractor hood does not therefore itself comprise a fan.

It is an object of the invention to embody an extractor hood such that the effectiveness with which the suction operation takes place is considerably improved.

In respect of this objective the invention provides an extractor hood comprising a housing for fixing to a building structure, for instance a wall, at a chosen position by means of fixing means, which housing (also) bounds a hollow space,- an outlet connecting to this space for drawing off air, vapour and the like entering the space via an inlet by means of a fan placed at a distance via a suction conduit for coupling to said outlet; and a plate (also) bounding this space on the underside and having a generally downward convex form, which plate together with the side walls of the housing defines with its front side and both side parts three optionally mutually connecting vents forming the said inlet .

Attention is drawn to the fact that "convex" form is understood to mean a plate of which in any case the side edges have a raised position relative to the middle part via a rounded, convex transition zone. This middle part can also be concave but also substantially flat.

In a particular embodiment the extractor hood comprises a control button which is coupled to control

means which can simultaneously control two functions. The one function relates to switch-on, switch-off or placing in a desired intermediate position of the extractor fan placed at a distance and driven by an electric motor. The other function relates to closing of the said outlet by means of a valve during non-use of the extractor hood. Possible fan noise can thereby be prevented from penetrating into the relevant work area via the outlet opening. When the extractor hood is set into operation the relevant valve can be opened preferably in direct mechanical manner by operating the control button, optionally combined with switch-on or setting of the fan at an increased rotation speed.

In a specific embodiment the extractor hood according to the invention has the special feature that the fan is accommodated in the outlet conduit at a distance from the extractor hood. Such an embodiment can have the advantage of a low noise production.

In order to eliminate the drawback of having to install electric wiring the extractor hood can have the special feature that the fan is accommodated in the extractor hood.

The extractor hood preferably has the special feature that at least the components coming into contact with air or vapour for extracting are heat-resistant, fire-resistant and/or flame-extinguishing. A particular development of this principle has the special feature that components consist substantially of polypropylene (PP) filled with talcum. Another embodiment has the special feature that components consist substantially of metal. This latter embodiment can have the feature that the metal is stainless steel .

In order to obtain a very great impact resistance, scratch resistance and form retention, also at relatively high temperatures and the unfavourable climatological conditions in which an extractor hood has to operate, the extractor hood can have the special feature that components consist substantially of a

mixture of polycarbonate and ABS . This variant relates particularly to the front of the extractor hood and the control buttons arranged thereon.

A specific embodiment has the special feature that the outlet comprises a valve with a fixed valve seat and a valve body which can be placed by control means between an open and a closed position. The closed position corresponds with a rest position, the fully open position corresponds with a position in which the extractor hood is fully operational, for instance during cooking, while the position with limited passage represents a position with a comparatively low level of extraction.

The extractor hood preferably has the special feature that the control means are of mechanical type.

Such an embodiment can be very inexpensive and reliable.

A preferred embodiment has the feature that the valve body is carried by a resilient support arm and/or formed integrally therewith, this support arm being operated by the control means. The support arm can for instance be a plastic strip. Such a strip is naturally resilient and flexible in transverse direction of its main plane. The control means can for instance comprise a manually operated turning knob which co-acts with the support arm by means of an eccentric cam.

A reliable sealing of the valve in closed position is ensured with an embodiment in which the valve body presses under bias against the valve seat in the closed position of the valve. Particularly by making use of the above described structure with resilient support arm, this variant can be embodied in very simple and reliable manner.

The extractor hood preferably has the feature that the valve seat and the valve have annular co-acting contact surfaces.

This latter embodiment can advantageously have the special feature that the valve seat is placed downstream of the valve body and has a form narrowing in

the flow direction. As a result of this form the transmission of sound coming from a remotely placed fan is particularly found to be negligible.

A preferred embodiment in which the valve has a contact surface with the shape of a part of a sphere has the great advantage that this structure is to a large degree independent of the actual position of the spheri¬ cal contact surface. This allows large manufacturing tolerances while still retaining good operation of the valve.

Test results with a fan flow in the range of about 100-200 m ³ /h, corresponding with practical conditions of use, have demonstrated that the best extraction results are achieved with an embodiment in which the width of each vent amounts to (15 ± 10) mm. A preferred embodiment has the special feature that the width of each vent amounts to (15 ± 5) mm.

The extractor hood is preferably embodied such that all vents have substantially the same width. An embodiment in which the plate is removable has the advantage that the plate can be cleaned easily and that the interior of the housing, in particular the walls of the hollow space bounded thereby, are easily accessible for cleaning. A preferred embodiment has the special feature that the control means are adapted to control the valve and the drive of the fan.

It is noted that operation of the lighting means preferably takes place with a separate button. The invention will now be briefly elucidated with reference to the annexed figures of a random embodiment. In the figures: figure 1 shows a perspective view from the underside of an extractor hood according to the invention; figure 2 shows a perspective view of the extractor hood, wherein for the sake of clarity the bottom plate is drawn at a distance;

figure 3 shows a cross section through the bottom plate of figure 2; figure 4 shows a partly broken away perspective view of the extractor hood; figure 5 shows a longitudinal section through the extractor hood.

Extractor hood 1 comprises a housing 2 provided with a coating, for instance an enamel layer, and a stainless steel bottom plate 3 which together with side walls 4, 5 and the front wall 6 of the housing bounds the respective vents 7, 8, 9. Continuous holes 10, 11, are arranged in bottom plate 3 for passage of light coming from lamps. Arranged on the front side is a central control knob 12 which is rotatable and thus co-acts mechanically via an eccentric transmission 13 (see figure 5) with a convex valve plate 14 which can co-act sealingly in the manner shown in figure 5 with a valve seat 15 which widens in downward direction and which co- acts sealingly with a discharge pipe end part 16. A push- button 24 operates the lamps.

As shown in figure 2, the holes 10, 11 are covered with transparent windows 22, 23.

Figure 3 shows a possible dimensioning of bottom plate 3. Figure 2 shows this bottom plate 3 in perspective view. It will be apparent from this view that plate 3 has at least partially a substantially prismatic form, i.e. has the same shape in any cross section. At the front and rear however, the plate has downward directed edges 20 and 21 respectively. Figure 4 shows schematically with arrows the flow of air drawn in via pipe end part 16. This passes through the three mutually connecting vents 7, 8, 9, moves through the hollow space 17 in housing 2 and leaves this hollow space via pipe end part 16. Control means and lamps are accommodated in an inner housing 18. Plate 3 is suspended in hooking manner with its rear edge 25 from the rear side of housing 2. At the front side it is fixed to the housing with screwable fastening bolts 26, 27.

The extractor hood shown in the figures does not comprise a fan. This is arranged at a distance in an outlet conduit coupled to pipe end part 16. The operation of the fan can be stationary, for instance in the case where the fan also serves for ventilation of a house, in which case the extractor hood is included in the extrac¬ tion circuits or removed therefrom by operating the valve 14, 15. By means of an electrical switch 28 controllable by knob 12 the remotely placed fan can be switched on and, if desired, be placed in different positions corre¬ sponding to different flow rates.

In a preferred embodiment in which this latter principle is implemented, the fan is either switched off or is set to relatively low operation while valve 14, 15 is closed. In an intermediate position the fan is placed in operative position or in a state of increased excita¬ tion and valve 14, 15 is closed. The fan then draws off the normal quantity of air via circuits other than via the extractor hood. In the cooking position the fan is in its highest state of excitation and valve 14, 15 is opened. The fan hereby draws off a relatively large amount of air, a large part of which comes from the extractor hood and a normal quantity of air from other inlet points.