GB2129109A - Domestic tumble drier - Google Patents

Abstract

In a tumble drier having a rotatable laundry drum 5 arranged in a cabinet 1, both the wall 3 of the cabinet and the end 6 of the drum are protected from direct heating by heating elements 15 by a baffle plate 12 and an annular shield 27 respectively. The plate 12 and shield 27 are so shaped that cool air can pass over the outer surface of plate 12, through an annular gap 13 which guides the air over the heating elements 15, then past a thermostat 28 before it reaches perforations 16 in the drum end 6. The possibility of any damage to laundry in drum 5 due to overheating of elements 15 is eliminated by the shielding of the drum end and the rapid response of the thermostat 28 to changes in the output of the elements 15. <IMAGE>

Description

SPECIFICATION Domestic tumble drier This invention relates to a domestic tumble drier comprising a rotatable laundry drum mounted in a cabinet, a heater and a fan which causes an air stream to pass over the heater and through the drum from one end to the other thereof, which heater is situated between said one end of the drum and an adjacent wall of the cabinet and is mounted on a baffle plate arranged between the heater and said wall, the arrangement being such that, before passing over the heater, at least some of the air stream passes over a major portion of the surface of the baffle plate facing said wall and thence through an annular gap formed between the peripheral edge region of the plate and the one end of the drum.

Such a tumble drier is known from United Kingdom Patent Application No. 2,095,806A. The plate provides two advantageous features; namely it prevents heating of the wall of the cabinet by direct radiation from the heater and it preheats the air before the air passes through the gap and over the heater.

Further, the plate is cooled by the passage of the cool air over its surface facing the wall.

The said patent application also discloses a tumble drier in which the heater is connected to a thermostat which is responsive to the temperature of the baffle plate. The thermostat disconnects the heater if the plate rises above a given temperature and hence protects the drier and any laundry in the drum from possible damage in the event of restriction of the air flow due, for example, to excessive lint on the lint filter, overloading of the drum, or blocking of the outlet duct from the machine.

It has now been realised, however, that due to the relatively large thermal capacity of the baffle plate the thermostat may be relatively slow to operate if the air flow is inadvertently stopped or reduced. It is then possible in some cases for laundry in the drum which may be in contact with the said one end of the drum to be scorched or otherwise damaged due to heating of a portion of that end by direct radiation from the heater.

Further, if that end is provided with air inlet perforations in the region of the heater, the laundry may be affected by direct radiation from the heater.

The object of the invention is at least to reduce the possibility of such damage to the laundry.

Accordingly the invention provides a domestic tumble drier of the type defined in the opening paragraph hereof, characterised in that the one end of the drum carries an annular metal shield arranged to shield said one end from direct radiation from the heater, and in that the heater is connected to a thermostat which is responsive to the air temperature downstream of the heater between the baffle plate and the shield.

The annular shield shields the drum end from direct heat radiation from the heater, whilst also serving to distribute the radiated heat over a relatively large area by thermal conduction and convection. Since the thermostat is responsive to the temperature of the air in the region of the heater, it operates to disconnect the heater much more rapidly than if it only responds to the temperature of the baffle plate. In this manner the possibility of any thermal damage to the drier or the drum contents is substantially eliminated.

If the annular shield is secured around its outer periphery to the drum and a major portion of the shield is spaced from the one end of the drum, and if the one end of the drum is provided with perforations in the region of the shield, at least a portion of the warmed air stream passes between the shield and the said one end of the drum. In this way, the shield increases the length of the warmed air path, thereby giving improved mixing of the air so that there is a more uniform air temperature reaching the laundry.

The tumble drier may be of the so-called suction, or vacuum, type in which the fan is arranged between the drum and the air outlet vent in the cabinet, whereby the air is sucked through the drum. Such a drier is described in the said patent application. It may alternatively be of the so-called pressure, or pressurized, type in which the fan blows air through the drum.

Embodiments of the invention will now be described with reference to the accompanying drawings, of which: Figure 1 shows a tumble drier of the suction type, Figure 2 shows, on a larger scale, a portion of the tumble drier shown in Figure 1 including the thermostat, and Figure 3 shows a tumble drier of the pressurized type.

The tumble drier shown in Figures 1 and 2 comprises a cabinet 1 having a front wall 2 and a rear wall 3. A door 4 is mounted on the front wall 2 and is openable to give access to the interior of a rotatable drum 5 which is provided at its rear end wall 6 with a central pivot 7 (shown schematically only) to enable the drum to be rotated about its horizontal axis by a motor 8 via a belt or other drive means (not shown).

Motor 8 also drives an impeller fan 9 which draws air into the cabinet via inlet apertures 1 1 in rear wall 3, over the rear surface of a circular baffle plate 12 centrally fixed to the rear wall, through an annular gap 13 formed between the periphery of the baffle plate 12 and an annular projection 14 on the rear end wall 6 of the drum 5, over a pair of substantially circular heating elements 1 5, through apertures 1 6 in the rear wall 6 of drum 5, through the drum and any laundry therein, through an annular gap 17 formed between the door 4 and an annular lip 18 on the front end wall 1 9 of the drum 5, through a perforated protection flange 21 on door 4, through a suction duct 22 surrounding door 4, and through impeller fan 9, whereafter the drawn-in air is expelled from the cabinet via an outlet duct 23 and an outlet vent 24.In the embodiment shown, air is also drawn into the cabinet 1 via an inlet vent 25 in the front wall 2. The general directions of air flow in the cabinet are shown by arrows in Figure 1. Inlet apertures 11 are preferably louvred as shown in Figure 2.

For the purpose of ease of understanding the air flow, the embodiment shows the air inlet vent 25 in the front wall of the cabinet and the outlet vent 24 in the rear wall. It is to be understood that vent 25 is optional both as to its provision and location.

Vent 24 may alternatively be located elsewhere in the cabinet, for example at the bottom of the front wall 2 of the cabinet.

If it is assumed, for the purpose of explanation, that the air inlet apertures 1 1 were not provided, the heat transferred to the baffle plate 12 from the heating elements 15 would serve largely to heat the rear wall 3. Thus the heat would not only be wasted but could also cause over-heating of the rear wall and possible consequent damage to adjacent equipment. The provision of inlet apertures 11 overcomes both these problems.

Firstly, the cool air passing over the rear surface of baffle plate 12 keeps the plate relatively cool and substantially prevents any rise in the temperature of the rear wall. Secondly, the heat in the plate is used to pre-heat the air entering the annular gap 13 and, therefore, is not wasted. Thus the efficiency of the drier is increased.

It is to be understood that some of the details which are generally known in tumble driers but which are not relevant to the invention are not shown in the Figure. Thus, for example, the door is provided with an air-tight seal to the front wall of the cabinet to prevent air being drawn in through the gap therebetween. Also, the front end of drum 5 is rotationally supported by the annular lip 18 riding on an annular flange 26 forming part of the suction duct housing.

An annular metal shield 27 is fixed, for example by rivets 33 (Figure 2) or by spot welds, around its outer peripheral edge to the projection 14 on the rear end wall 6. Although the shield 27 may be located close to the rear end 6 over most of its surface area, it is preferably spaced from the end 6 over the major portion of its surface as shown in Figures 1 and 2. In this case, some of the air passes through the space between the shield 27 and the end 6 of the drum and thence through perforations 16, as shown by the arrows. This passage of air reduces heating of the end 6 in the region of shield 27 by any direct radiation from the shield 27.

The temperature of the air stream passing between baffle plate 12 and shield 27 is sensed by a thermostat 28 which operates to disconnect the electrical supply to the elements if the temperature rises above a given value, e.g. 1 500C, in the range 1 300C to 1 70 C. Thermostat 28 is secured to plate 12 and is thermally insulated therefrom by a layer 29 (Figure 2) of insulating material and therefore operates relatively rapidly in the event of over-heating to prevent any thermal damage to the tumble drier or to any laundry in the drum 5.

Figure 2 also shows a thermal overload cut-out 31 which is mounted on a locally flattened extension portion 32 of the baffle plate 12. Due to this local flattening of plate 12, the annular air gap 13 is wider in the immediate region of cut-out 31 and so the flow of air through the gap is not noticeably reduced in this region. Such an arrangement eliminates the possibility of any "hot spot" on heating elements 15 in this region. The cut-out 31 provides an additional safety feature by protecting the laundry load against a complete failure of the air flow, e.g. a drive motor failure or a total blockage of the outlet duct. In normal use cool air passes over this cut-out but if the air flow ceases then hot air from the heating elements 1 5 pass over it and causes it to operate, for example at 145 C.

Figure 3 shows an embodiment of a pressurized type of tumble drier in which items corresponding to items shown in Figures 1 and 2 are given the same reference numerals.

In this case, fan 9 draws air into cabinet 1 via inlet 25 in the rear wall 34 of the cabinet 1. The only outlet for the air forced into the cabinet via fan 9 is via perforations (not shown) in the door 32, and so there is a build up of air pressure inside the cabinet. The cool air from fan 9 can circulate freely in the space between baffle plate 12 and the rear wall 34 of the cabinet. The air is forced through the annular gap between the drum projection 14 and the periphery of baffle plate 12, through the perforations 16 in the rear end 6 of the drum 5, through a laundry load in the drum, and is then vented via the perforations in door 32, usually via a lint filter, not shown.

The arrangement of the baffle plate 12, heater elements 15, annular shield 27, thermostat 28, thermal cut-out 31 and extension 32 of plate 12 are as shown in Figure 2. In this case, however, the rear wall of the cabinet is not provided with any air inlets 11.

Although the embodiments described with reference to the accompanying drawings relate to front-loading driers, it will be clear that the invention is equally applicable to a drier of a toploading kind. For a top-loading drier, access to the drum could be obtained through a door located in the top surface of the cabinet and a second door located in the curved surface of the drum. The ends of the drum could lie close to the respective side walls of the cabinet, and the plate carrying the heater would be located between one of these ends and the adjacent cabinet side wall.

Claims (4)

1. A domestic tumble drier comprising a rotatable laundry drum mounted in a cabinet, an electric heater, and a fan which causes an air stream to pass over the heater and through the drum from one end to the other thereof, which heater is situated between the one end of the drum and an adjacent wall of the cabinet and is mounted on a baffle plate arranged between the heater and said wall, the arrangement being such that, before passing over the heater, at least some of the air stream passes over a major portion of the surface of the baffle plate facing said wall and thence through an annular gap formed between the peripheral edge region of the plate and the one end of the drum, characterised in that the one end of the drum carries an annular metal shield arranged to shield the said one end from direct radiation from the heater, and in that the heater is connected to a thermostat which is responsive to the temperature of the air downstream of the heater between the baffle plate and the shield.

2. A domestic tumble drier as claimed in Claim 1, wherein the shield is secured around its outer periphery to the drum with a major portion of the shield spaced from the one end of the drum, and wherein the one end of the drum is provided with perforations in the region of the shield whereby at least part of the warmed air stream passes between the shield and the said one end.

3. A domestic tumble drier as claimed in Claim 2, wherein the thermostat is operable at a selected àir temperature in the range from 1 300C to 1 7000 to disconnect the heater.

4. A domestic tumble drier as claimed in any previous Claim, wherein a thermal overload cutout is arranged in the air stream path upstream of the heater and is so located with respect to the heater that if, in operation of the heater, the flow of air over the heater is strongly impeded or ceases, the cut-out is heated by the heater and operates to disconnect the heater.