Patent Description:
From the state of the art tumble dryers are known which heat the airflow and guide the same through laundry to be dried so that the heated airflow absorbs the humidity of the laundry. There are known, for example, vented dryers which vent the humid airflow afterwards to the environment. Furthermore, dryers including a condenser are known for example, wherein the airflow is dehumidified again in the condenser so that the airflow then can be reheated in a circuit and can be circulated through the laundry again.

The airflow may be heated in a separate housing which is integrated in a rear wall of the tumble dryer.

In <CIT> a clothes treating apparatus is disclosed comprising a module mounted onto an outer surface of a cabinet. The module comprises a heater assembly and a blower assembly. A housing of the heater assembly has a slit through which external air is introduced and added to the air heated by the heating assembly. The external air is taken from a space between the inner housing of the heater assembly and an outer housing of the module.

In the patent specification <CIT> such heating device integrated in the rear wall of a tumble dryer is disclosed. It includes a trough-like housing forming a portion of the rear wall of the tumble dryer. A heat shield in which the heating elements are accommodated is inserted in the housing. The airflow to be heated is guided through the heat shield and hence through the heating elements.

It is a drawback of said heating devices that the temperature of the housing constituting the outer wall of the tumble dryer in question can get hot in spite of the heat shield member which means a significant energy loss of the heating devices via the outer wall.

<CIT> discloses a tumble dryer with a rear wall, whereby at the inner side of the rear wall heater elements and a baffle plate are provided. Cool air from a fan can circulate freely in a space between the rear wall and the baffle plate. This keeps the rear wall relatively cool.

<CIT> discloses a cloth drying machine comprising a door in which an air heating device is accommodated. At a lower part of the door an inlet for external air is located. A portion of the external air can flow between an outer sheet metal component of the door and an inner heat reflector.

Compared to this, the object underlying the invention is to provide a heating device and a tumble dryer which is more sensitive to a safety situation where overheat could occur due to loss of airflow.

This object is achieved by a heating device comprising the features of claim <NUM> and by a tumble dryer comprising the features of claim <NUM>.

The claimed heating device includes a housing configured to be mounted on a housing wall - preferably rear wall - of a tumble dryer. Inside the housing of the heating device a heating arrangement which may be formed by plural heating coils is accommodated. A main airflow to be heated is guided through the heating arrangement. Moreover, a heat shield is inserted in the housing between the heating arrangement and the housing. At least one aperture is provided which permits bypass airflow or air bleed branched off or discharged from the total airflow. The bypass airflow or air bleed is not guided through the heating arrangement so that its temperature is lower than that of a main airflow guided through the heating arrangement. Thus the bypass airflow or air bleed cools the housing so that the risk of burns for users is definitely reduced. The bypass airflow or air bleed acts as a thermal insulator reducing heat loss through the rear wall and improving the efficiency of the heating device. In addition, also the risk of harmful heat impact on e.g. power cables or plastic tubes of a tumble dryer in question which are (maybe accidentally) in contact with the outside of the housing is definitely reduced.

According to the invention, it is simple when the housing includes a full-surface main wall and when the heat shield equally is a full-surface member so that it is arranged adjacent and preferably approximately in parallel to the main wall. The main wall and the heat shield are spaced from each other and thus define a cross-section of the aperture.

According to the invention, a temperature sensor and a thermostat are designed for lower temperatures and are cooled by the bypass airflow. For this reason the heating device is more sensitive to a safety situation where overheat could occur due to loss of airflow.

Further advantageous configurations of the invention are described in the dependent claims.

The heat shield serves as a separating element between the main airflow (on one side) and the bypass airflow or air bleed (on the other side).

For efficient cooling it is sufficient when the branched-off bypass airflow is considerably smaller than the main airflow, i.e. when the bypass airflow amounts to e.g. less than <NUM> % of the main airflow.

The aperture is provided between the heat shield and the housing.

The heat shield can be further developed to constitute a two-sided heat protection member.

The distance between the main wall and the heat shield and thus the cross-section of the aperture can be defined, in terms of devices, simply by at least one projection, especially by plural projections. The projection(s) extend(s) from the main wall toward the heat shield so that the heat shield contacts the projections.

Further a bulge extending outwardly and approximately transversely to the two airflows is preferred on the main wall. In this way the stability of the main wall of the e.g. deep-drawn housing is increased. The bulge is preferably disposed in the area of the heating arrangement, preferably in parallel to the heating coils thereof.

The bulge is preferably arranged approximately centrally between at least one upstream projection and at least one downstream projection.

The heating device according to the invention includes the temperature sensor or the thermostat arranged downstream of the heat shield. Then the bypass airflow can reach the temperature sensor or thermostat so that the latter has to be designed for lower temperatures. When the temperature sensor or thermostat is arranged in an area of the housing spaced apart from the heat shield, the thermal load of the temperature sensor or thermostat can be further reduced. Additionally the temperature sensor or thermostat can be designed for lower temperatures which means it is more sensitive to a safety situation where overheat could occur due to loss of airflow.

When the temperature sensor is mounted on a flow deflecting element (e.g. a baffle) inserted downstream of the heat shield or in the area of the housing spaced apart from the heat shield into said housing, the temperature sensor may protrude on the rear side from the flow deflecting element into a free space and the free space creates space for power cables.

Preferably the flow deflecting element is inclined relative to the main wall so that the two airflows are guided away therefrom and are deflected in the direction of the tumble dryer. Especially also the bypass airflow is guided via the baffle, as it flows along the main wall. Thus the portion of the bypass airflow reached by the temperature sensor is large. In this way the thermal load of the temperature sensor can be further reduced. Additionally the temperature sensor can be designed for lower temperatures which means it is more sensitive to a safety situation where overheat could occur due to loss of airflow.

At the flow deflecting element a temperature limiter and/or the thermostat may be arranged as well. They may protrude on the rear side into the free space due to the inclination of the flow deflecting element and space for power cables is created.

In terms of manufacture and especially in terms of safe electric insulation for the heating coils, it is of advantage when the heat shield is made of micanite.

In a further development at least one flat-shaped flow baffle which is inclined relative to a (respective) wall portion of the housing is provided upstream of the heating arrangement. Preferably the (respective) wall portion is perpendicular to the main wall. Thus the airflow extending along the respective wall portion is guided to the heating arrangement. The at least one flow baffle preferably is also made of micanite or of sheet metal.

According to a first variant, the heat shield is shorter than the heating arrangement or as long as the heating arrangement in the flow direction. In particular, the heat shield is shorter than the diameters of two neighboring heat coils including a distance between said two heat coils.

According to a second variant, the heat shield is longer than the heating arrangement in the flow direction and projects therefrom in and against the flow direction.

There may be provided e.g. three projections upstream of the heating arrangement and three projections downstream of the heating arrangement. Also, there may be provided, for example, three projections upstream and one projection downstream of the heating arrangement.

In a preferred development the heat shield is clamped between the projections and the heating arrangement, especially one or two outer heating coils. The heat shield may be slightly bent.

In a transition region from the main wall to the wall portion perpendicular thereto preferably screws by which the heat shield is mounted on the housing are inserted. Preferably also the heating arrangement is mounted on the housing via these screws.

In one configuration the housing has a border arranged approximately in parallel to the main wall. The border includes through-holes for fastening means, or fastening means by which the afore-described heating device can be fastened to the tumble dryer are disposed on the border.

The tumble dryer according to the invention includes a rear wall to which the border of the afore-described heating device is mounted.

In the figures several embodiments of a heating device according to the invention are illustrated. The invention will hereinafter be illustrated by way of the figures, in which.

<FIG> shows in a perspective sectional view a first embodiment of the heating device according to the invention. It comprises a trough-like housing <NUM> including an outer comparably large main wall <NUM> which turns into a circumferential wall portion <NUM> via a rounded transition region <NUM>. The circumferential wall portion <NUM> is approximately perpendicular to the main wall <NUM>. Via a further rounded transition region the peripheral wall portion <NUM> turns into a border <NUM> arranged approximately in parallel to the main wall <NUM>. The border <NUM> is mounted to a rear wall of the housing of a tumble dryer (not shown). Between the border <NUM> and the housing of the tumble dryer a seal <NUM> is provided.

In the housing <NUM> a heating arrangement <NUM> consisting of a total of four heating coils <NUM>, <NUM> is provided. Two heating coils <NUM> are arranged adjacent to the main wall <NUM> and are referred to as outer heating coils <NUM>, as in the mounted state of the heating device they are located on the outside. The two other heating coils <NUM> are referred to as inner heating coils <NUM>, as they are arranged adjacent to the tumble dryer.

Ambient air is sucked via an impeller of a fan (not shown) into the interior of the housing <NUM> according to the arrow shown in <FIG> and is delivered downwards by the heating coils <NUM>, <NUM>. Downstream of the heating coils <NUM>, <NUM> the total airflow is deflected via a flow deflecting element <NUM> (to the left in <FIG>) in the direction of an entry into the tumble dryer. The flow deflecting element <NUM> is inclined by approximately <NUM>° with respect to the main wall <NUM> and to the neighboring wall portion <NUM>. A temperature limiter <NUM> and a thermostat <NUM> are inserted in the flow deflecting element <NUM>. It is evident from <FIG> that due to the inclination of the flow deflecting element <NUM> a rear free space is formed into which the temperature limiter <NUM> and the thermostat <NUM> extend in portions.

<FIG> illustrates in a further perspective view the heating device according to <FIG>. It is evident that in addition to the temperature limiter <NUM> and the thermostat <NUM> a temperature sensor <NUM> is inserted in the flow deflecting element <NUM>.

The flow deflecting element <NUM> includes connecting portions <NUM> bent on both sides, each being connected to a retaining device <NUM>. Between the two retaining devices <NUM> the heating arrangement <NUM> is accommodated. Furthermore, a flow baffle <NUM> which is inclined with respect to the neighboring wall portion <NUM> and guides the total airflow upstream of the heating arrangement <NUM> in the direction of the heating arrangement <NUM> is fastened or formed upstream of each retaining device <NUM>.

<FIG> illustrates that an outer strip-shaped micanite element <NUM> and an inner strip-shaped micanite element <NUM> extend between the two retaining devices <NUM>, only one of which is shown in <FIG>. Both micanite elements <NUM>, <NUM> serve as heat shield and especially as electric insulation for the heating coils <NUM>, <NUM>. Both micanite elements <NUM>, <NUM> can be equal for the purpose of facilitating manufacture. Both micanite elements <NUM>, <NUM> extend transversely to the flow direction of the air approximately along the length of the four heating coils <NUM>, <NUM>.

In the flow direction of the air the micanite elements <NUM>, <NUM> have a width corresponding approximately to the distance of the central axes of the two outer heating coils <NUM> and consequently also to the distance of the central axes of the two inner heating coils <NUM>. Hence the two micanite elements <NUM>, <NUM> are shorter in the flow direction than the entire heating arrangement <NUM>.

<FIG> illustrates that one of the two inner heating coils <NUM> and one of the two outer heating coils <NUM> protrude in the flow direction of the air directed from the top to the bottom in <FIG> beyond the inner micanite element <NUM>.

<FIG> shows a perspective view of the trough-shaped housing <NUM> from outside. In the main wall <NUM> in the area of the heating arrangement (not evident from <FIG>) a bulge <NUM> extending approximately over the length of the heating coils <NUM>, <NUM> or the micanite elements <NUM>, <NUM> is provided transversely to the flow direction of the air. The bulge <NUM> is formed to be approximately roof-shaped having two flanks and is rounded at its ends. It extends outwardly, i.e. away from the outer micanite element <NUM>. It serves for stabilizing the main wall <NUM> of the housing <NUM> manufactured by a deep-drawing process.

Upstream and downstream of the bulge <NUM> three respective cam-shaped or approximately conical projections <NUM>, <NUM> are introduced to the main wall <NUM>.

Moreover, according to <FIG> two seats <NUM> for fastening screws (not shown) by each of which one of the two retaining devices <NUM> shown in <FIG> and thus the heating arrangement <NUM> are mounted on the housing <NUM> are provided in the rounded transition region <NUM> between the main wall <NUM> and the circumferential wall portion <NUM>.

<FIG> shows the central upstream projection <NUM> and the central downstream projection <NUM> in a sectional view. Each of said two projections <NUM>, <NUM> is arranged centrally between the two associated outer projections <NUM>, <NUM>.

The outer micanite element <NUM> is adjacent to all six projections <NUM>, <NUM>, thereby an aperture <NUM> for a bypass airflow being formed. According to the invention, the total airflow is divided in two from an air inlet (not shown) to the flow deflecting element <NUM>. More exactly speaking, a larger inner main airflow heated by the heating arrangement <NUM> is formed between the two micanite elements <NUM>, <NUM> and a smaller outer bypass airflow not or hardly heated by the heating arrangement <NUM> is formed through the aperture <NUM>, viz. between the outer micanite element <NUM> and the main wall <NUM>. Thus the bypass airflow continues flowing along the main wall <NUM> also to the flow deflecting element <NUM> and thus especially acts also on the temperature limiter <NUM>, the thermostat <NUM> and the temperature sensor <NUM>, the latter being configured with negative temperature coefficients (NTC). In this way, said components <NUM>, <NUM>, <NUM> can be designed for lower heat and thus by simpler devices without the monitoring and control of the heating of the total airflow being impaired. Especially the thermostat <NUM> and the temperature sensor <NUM> can be designed for lower temperatures which means they are more sensitive to a safety situation where overheat could occur due to loss of airflow.

When the temperature limiter <NUM> is heated above a predetermined temperature, it responds so that the heating arrangement is switched off.

<FIG> illustrates in a cut perspective representation a second embodiment of the heating device according to the invention. The substantial difference from the first embodiment according to <FIG> has to be perceived in the fact that the inner micanite element <NUM> and the outer micanite element <NUM> are broadened in and against the flow direction and thus their width is more than doubled. In this way the two micanite elements <NUM>, <NUM> surmount the two flow baffles <NUM> made of sheet metal against the flow direction and extend approximately up to the air inlet. Also downstream of the heating arrangement <NUM> the micanite elements <NUM>, <NUM> are extended and surmount the heating arrangement <NUM>.

Being adapted to the broadening of the outer micanite element <NUM>, also the three upstream projections <NUM> and the merely single downstream projection <NUM> in this embodiment are positioned at a respective border area <NUM>, <NUM> of the outer micanite element <NUM>. The outer micanite element <NUM> is clamped between the outer heating coils <NUM> and the projections <NUM>, <NUM> so that the upstream border area <NUM> and the downstream border area <NUM> of the outer micanite element <NUM> are inwardly bent. A central main section <NUM> of the outer micanite element <NUM> is tensioned in the direction of the main wall <NUM> by the two outer heating coils <NUM>.

<FIG> shows in a perspective representation viewing approximately along the flow direction the second embodiment according to <FIG>. It is evident in which way the upstream border area <NUM> of the outer micanite element <NUM> is tensioned by the three upstream projections <NUM> of the main wall <NUM> in the direction away from the main wall <NUM>, thus the size of the entry of the aperture <NUM> being defined.

In another perspective representation <FIG> illustrates the outside of the housing <NUM>. Accordingly, the distance of the upstream projections <NUM> from the downstream projection <NUM> is evident which corresponds approximately to the extension of the inner micanite element <NUM> and moreover also of the outer micanite element <NUM>.

In both embodiments according to <FIG>, each of the bulge <NUM> and the projections <NUM>, <NUM> are manufactured as embossing.

Claim 1:
A heating device comprising a housing (<NUM>; <NUM>) which is configured for being attached to a housing wall of a tumble dryer, wherein a heating arrangement (<NUM>) for heating a main airflow is accommodated inside of the housing (<NUM>; <NUM>), whereby in said housing (<NUM>; <NUM>) at least one aperture (<NUM>; <NUM>) is provided through which a bypass airflow is allowed, the temperature of said bypass airflow being below that of the heated main airflow, wherein the heating device includes a flat-shaped heat shield (<NUM>; <NUM>), wherein the housing (<NUM>; <NUM>) includes a main wall (<NUM>) being arranged adjacent to the heat shield (<NUM>; <NUM>) and confining the aperture (<NUM>; <NUM>) together with the heat shield (<NUM>; <NUM>), characterized by a temperature sensor (<NUM>) and a thermostat (<NUM>), which are located downstream of the heat shield (<NUM>; <NUM>), and which are cooled by the bypass airflow.