GB2145926A - Coffee machine - Google Patents

Abstract

A coffee machine comprises a centrifugal filter (22) which is detachably coupled to a motor drive shaft (16) and receives water for brewing by means of a co-rotatable conveying device (24) arranged thereat from a heated water bowl (8) arranged under the filter. In order to avoid imbalances and ensure even distribution of the water to the ground coffee and good utilisation of the coffee, the conveying capacity of the conveying device is so related to the shape and size of the filter (22) and of an outlet (56) of the filter that, in use of the machine with fine to medium grade coffee, water conveyed into the filter by the conveying device accumulates inside a ring (52) of centrifuged coffee in the filter. Water may completely fill the filter, and may also accumulate in the conveying channels. Water discharge outlets may have a smallest dimension of up to 0.01-0.5mm. <IMAGE>

Description

SPECIFICATION Coffee machine The present invention relates to a coffee machine.

In a coffee machine in which water conveying equipment and a centrifugal filter rotate without movement of one relative to the other, the problem exists that the conveying equipment sprays water for brewing unevenly over the ring ofground coffee which forms in the filter. This leads to imbalances and uneven utilisation ofthe ground coffee. Moreover, to avoid rotational imbalances it is necessary to centre the filter together with the conveying equipment relatively precisely on a motor drive shaft without the centring devices requiring especially close tolerances that are expensive to produce.

There is accordingly a need for a coffee machine in which imbalances may be avoided, with the water for brewing being evenly distributed to the ground coffee and with good utilisation ofthe ground coffee.

According to the present invention there is provided a coffee machine comprising a motor having a drive output shaft, a centrifugal filter drivably and detachably coupled to the shaft, and conveying means arranged at the filter to be rotatable therewith to conveywaterthereto, the conveying means being provided with a plurality of conveying channels distributed around its circumference and the conveying capacity of the conveying means being so related to the shape and size ofthe filter and of outlet means of the filter that, in use ofthe machine with a sufficient quantity offineto medium grade coffee, the coffee is centrifuged in front of the outlet means to form a ring providing such resistance to flowtherethrough of water conveyed into the filter by the conveying means as to cause an accumulation of such water within the space enclosed by the ring of centrifuged coffee.

In this manner, during the greater part ofthetime of the passage of the waterthrough the centrifugal filter, a uniformly distributed ring of water is disposed therein, in which the ground coffee is received and so that imbalances do not occur even in the case of uneven distribution of the coffee in the filter.

Preferably, the aforesaid matching is such that the centrifugal filter is filled completelywith water for brewing. The conveying equipmentthus possesses a substantially greater conveying capacity than the centrifugalfilterwith a normal filling of ground coffee, so that the outward conveying of the brewed coffee depends only on the actual filteratthe outer cir- cumference of the centrifugal filter and on the resistance of the layer of ground coffee. In this way it is ensured that the ground coffee is always disposed in the accumulated water.

The conveying equipment is preferably closed off at a delivery end thereof except for one or more delivery openings, wherein the minimum clearwidth of the delivery opening at no point ofthe opening is greater than about 0.01 to 0.5 millimetres. Consequently, if the motor is switched off too early, the ground coffee particles are prevented from being washed through the delivery openings back into the conveying equipment andfinally into the water bowl. The ground coffee blocks in the opening or openings and largely obstructs the coffee disposed in the filterfrom flowing back into the conveying equipment and the water bowl.

Preferably, the minimum clearwidth is about between 0.01 and 0.3, particularly between 0.01 and 0.05 millimetres, whereby a return flow of ground coffee is prevented to the largest extent. The delivery opening may be provided by an annular gap extending around the rotational axis ofthe conveying equipment, in particular a hollow cone ofthe conveying equipment and a lid placed on the upper end of the cone, in which casethesurfaceunevennessesof the parts suffice to obtain an adequate annular gap when the parts are set one againstthe other.

Advantageously, the total cross-sectional area ofthe delivery opening or of all delivery openings is such that a certain build-up ofthe brewing water occurs in the conveying equipment. This build-up leadsto a uniform distribution over all delivery openings, or overthe entire length ofthe annular gap, and thereby to a uniform loading ofthe ground coffee lying in the actual centrifugal filter around the conveying equipment, which is particularly important during the starting phase.

An embodiment ofthe present invention will now be more particularly described by way of example and with reference to the accompanying drawings, in which: Fig. is a sectional elevation of a coffee machine according to the said embodiment, a centrifugal filter ofthe machine being shown in section along the line 1-1 of Fig. 2; and Fig. 2 is a cross-section, to an enlarged scale, along the line ll-ll of Fig. 1.

Referring nowthe drawings, there is shown an electric coffee machine comprising a pot-shaped pedestal housing 2 with a stand platform 4, formed laterally thereat, for two coffee cups 6 one beside the other. Resting on the housing 2 is a water bowl 8 having a base 10which drops away towards the centre and atthe underside ofwhich is arranged an electric heater 12. In the central region, the base 10 passes over into a stub pipe 14, which projects upwardly in the bowl and through which extends a vertical shaft 16 of an electric motor 18. The motor is retained by carriers 20, which are formed at the underside ofthe base 10 of the bowl 8.

The machinefurthercomprisesa centrifugal filter 22 with an upwardly widening hollow cone 24, which projects downwardly into the bowl 8 and serves as conveying equipmentforwaterfor brewing. Fastened to the motor shaft 16to be secure against rotation relativethereto is an entraining member25,the outside shell ofwhich slightly conical Iy widens downwardly and projects beyond the stub pipe 14 of the bowl 8 as far as into the base region ofthe bowl.

The cone 24 has three centering ribs 27 which project from its inside and extend over its entire height. The inside edges of the ribs 27 have the same conicity relative to the axis of rotation as the outside shell of the entraining member 25 and are pressed from above onto this shell. A respective further rib 28, which does not project quite as far as the outside shell of the entraining member 25, is disposed between each two adjacent centering ribs 27. The additional ribs 28, not serving for centering, co-operate with the ribs 27 to form a number of vertical conveying channels in the cone 24 in orderto provide as uniform as possible a distribution of the conveyed water around the circumference.

The cone 24 is closed off upwardly by a lid 29, whilst an annular gap 54forthe delivery ofthewateronto the ground coffee in the filter remains between the cone 24 and the lid. The lid 29 is anchored to be secure against rotation at the ribs 27 and 28 and at its inside possesses a coupling toothing which is indetachable engagement with a coupling toothing 26 atthe upper end ofthe entraining member25.

Sitting on the upper rim ofthe bowl 8 is a collecting chamber member 30 in the form of an annular gutter having a bottom 32 dropping away towards the stand platform 4 and an outlet channel 34. The channel 34 projects substantially radially outwards and branches into two outlets 36, only one which can be seen in the drawing.

Resting on the member30 isa lid 38 with a transparent downwardly projecting cylindrical annularwall 40, which extends into the member 30, catches the coffee centrifuged out of the filter 22 and conducts it down into the annular collecting chamber.

In use of the coffee machine, with the lid 38 taken off and the centrifugal filter 22 drawn offthe shaft 16, fresh water is poured from above into the bowl 8.

Then, after removal of a lid 50 ofthefilter22, ground coffee 52 is placed in the filter. Finally, the filter is plugged onto the entraining member 25, the lid 29 engaging the coupling toothing 26,the lid 38 is placed on the member30, and two cups 6 are set on the platform 4 belowthe outlets 36. The heater 12 is switched on through actuation of an on-off switch 60.

Atemperature sensor (not shown) arranged at the bowl 8 actuates a signal lamp 62 as soon as the brewing temperature is reached. The machine is thus in a state of readiness and the user can, as soon as it is desired to fill the cups, setthe motor 18 into motion through actuation of a key switch 64.As a result,the filter 22 is accelerated and the ground coffee 52 is at first distributed annularly as illustrated. As soon as a sufficiently high rotational speed is reached, the cone 24 begins to convey and acceleratesthewaterfor brewing through the annular gap 54 at its upper end and onto the ring 52 of ground coffee.The prepared coffee issues from the filter 22 through an annular gap 56, is caught by the annularwall or collecting wall 40 of the lid 38 and is conducted downwardly into the collecting chamber member30, from where itflows through the channel 34with a distributor equipment arranged therein and the outlets 36 into the coffee cups 6.

The coffee generates a structure on the transparent annularwall or collecting wall 40 which is visible from outside and which alters noticeably when only a little orvirtually no coffee is being issued. The user can stop the motorthrough release of the key switch 64. The last amount of issuing coffee requires a moment until it hasflowed down the annularwall 40 and through the collecting chamber, the channel 34, the distributor and the outlets 36 into the coffee cups 6. The coffee issuing or accelerating processlastsabout35to40 seconds and the user holds the key switch 64 pressed during this time.

The horizontal annular gap 54 between the underside ofthe lid 29 and the upper edge of the hollow cone 24 serving as conveying equipment possesses a gap width or clear width of 0.03 millimetres. From the bottom of the chamber receiving the groundcoffee 52, the annular gap has a spacing of about 1/3 ofthe heightofthis chamber.

The annulargap54atthe delivery end ofthe conveying equipment, the annular gap 56 at the outside of thefilter 22,the geometry of the filter and the resistance resulting therefrom ofthe ground coffee layer disposed therein are so matched to each otherthat, on the use ground coffee offine or medium grade, build-up ofwaterarises atthe ground coffee layer52. Thus, during a large part ofthe brewing process, a ring ofwaterfor brewing is disposed within the ring of ground coffee, i.e. in front ofthe ground coffee as seen in radial direction. As a result, a high extraction content from the ground coffee, i.e. a good utilisation ofthe ground coffee, is achieved. A definition of the degree grades of ground coffee is provided in German (Fed. Rep.) published patent specification 27 55 014, column 1, lines 47 to 55, together with an indication of the quantity of coffee to be used per cup.

Preferably, the matching of the afore-mentioned parameters influencing the filling ofthe filter with water is such that the filter, for the major part of the filtering operation, is entirely filled with water and a build-up ofthewaterarises in the conveying equipment, preferably up to the suction side thereof. The speed ofthe conveying is in this case determined by the dimensions ofthe filter gap 56 and the throughflow resistance ofthe layerofground coffee. The annular gap 56 represents the actual filter.

The coffee machine hereinbefore described is also described in the specification of United Kingdom patent application No.8225038.

Claims (8)

1. Acoffee machine comprising a motor having a drive output shaft, a centrifugal filter drivably and detachably coupled to the shaft, and conveying means arranged at the filterto be rotatable therewith toconveywaterthereto,theconveying means being provided with a pluralitsof conveying channels distributed around its circumference and the conveying capacity ofthe conveying means being so related to the shape and size of the filter and of outlet means of the filter that, in use of the machine with a sufficient quantity offine to medium grade coffee, the coffee is centrifuged in front of the outlet means to form a ring providing such resistance to flowther through otwater conveyed into the filter bythe conveying means as to cause an accumulation of such water within the space enclosed by the ring of centrifuged coffee.

2. Acoffee machine as claimed in daim 1,wherein said relationship of the conveying capacitytothefiiter and outlet means shape and size is such that the filter is completelyfillable with such conveyed water.

3. Acoffee machineas claimedin either claim 1 or claim 2, the conveying means being closed at an end thereof which is downstream in the conveying direc tion and being provided at said closed end with at least one delivery opening for delivery of conveyed water into the filter, the minimum clearwidth ofthe or each delivery opening being at most substantially 0.01 to 0.5 millimetres.

4. Acoffee machine as claimed in claim 3,wherein the minimum clearwidth ofthe or each delivery opening is substantially 0.01 to 0.3 millimetres.

5. A coffee machine as claimed in claim 4, wherein the minimum clearwidth of the or each delivery opening is substantially 0.01 to 0.05 millimetres.

6. A coffee machine as claimed in any one of claims3to 5, wherein the delivery opening is provided by an annular gap extending around the rotational axis ofthe filter.

7. Acoffee machine as claimed in any one of claims 3to 6, wherein the total cross-sectional area of the delivery opening or openings is so selected that, in use of the machine, conveyed water accumulates in the conveying means.

8. A coffee machine as claimed in claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.