WO2000019873A1

WO2000019873A1 - Improvements relating to electric water heating appliances

Info

Publication number: WO2000019873A1
Application number: PCT/GB1999/003298
Authority: WO
Inventors: Robert Andrew O'neill; John Anthony Howarth
Original assignee: Otter Controls Limited
Priority date: 1998-10-06
Filing date: 1999-10-06
Publication date: 2000-04-13
Also published as: GB9821769D0; GB2343352A; GB9923658D0; AU6113099A

Abstract

A beverage percolator has a thick film heating element with a spiral main heater track occupying only about a quarter of the area of the heating element at a central position thereof and a keep-warm heater track surrounding and spaced from the main heater track. A thermostat monitors the temperature of the heating element at a position traversed by the keep-warm track and is arranged to connect the keep-warm track, which is normally short-circuited by the thermostat, in series with the main track so as substantially to reduce the power output of the heater to about one-tenth of its power output when the keep-warm track is out of circuit, the reduced power output keeping the percolated beverage warm. The percolator is of the cordless type and has a 360° power input connector on the percolator vessel which is arranged to supply electricity to the heating element when the percolator vessel is seated on a base having a complementary 360° power input connector.

Description

IMPROVEMENTS RELATING TO ELECTRIC WATER

HEATING APPLIANCES

Field of the Invention:

This invention concerns improvements relating to electric water

heating appliances and particularly, though not exclusively, concerns

percolator appliances, for example for domestic use, wherein an electric heater

is arranged to heat to boiling a small volume of water which is expelled from

the boiling space and replaced by cooler water, the expelled water being

delivered by a pipe to a filter basket containing ground coffee or tea for

example which is infused by the hot water, the infusion being returned to the main volume of liquid to be recirculated through the boiling space so that the

infusion becomes progressively stronger and at the same time its temperature

increases.

Background of the Invention:

As described in our British Patent Application No. 9805568.4 filed

16 March 1998, the problem arises with conventional recirculatory ^~ type

percolators as described above that the time required for preparation of a

beverage is undesirably long, commonly of the order of 10 minutes to prepare

one to one and a half litres of beverage, on account of the fact that the power

of the heating element must be limited to ensure that the percolation activity

does not become excessively violent. To overcome the abovementioned problem, the proposal is made in

British Patent Application No. 9805568.4 to make use of a thick film heating

element having a plurality of heating areas and to associate a separate

percolator structure with each heating area. By virtue of such an arrangement,

simultaneous multiple percolator activities operate in parallel thereby enabling

overall percolation time to be reduced.

The present invention stems from further design and development

work that we have undertaken.

Summary of the Invention:

According to the present invention, a thick film heating element for a

percolator comprises a main heating element track for association with a percolator structure and a surrounding keep warm heating element track, the

main heating element track having a spiral form and having current supply

terminals at the ends of the spiral, and the keep warm heating element track

having one end connected to the outermost one of the terminals of the main

heating element track and having at its other end a terminal lying closely

adjacent to said outermost main heating element terminal, the arrangement

being such as to enable power to be supplied to the main heating element

track by way of a thermally-responsive control device coupled across the

terminal ends of the keep warm heating element track and arranged to short

circuit the keep warm heating element track until such time as the control

device goes open circuit when the heating element temperature rises to a predetermined level whereupon the keep warm heating element track is

connected in series with the main heating element track.

The invention may conveniently be embodied in a cordless percolator

appliance comprising a percolator proper and a base unit upon which the

percolator proper must be set for supplying electric power to the thick film

heating element in the percolator proper, there being complementary electrical

connectors on the percolator proper and on the base for enabling the

percolator proper to be powered via the base when it is set down on the base.

Advantageously the complementary electrical connectors are of a kind such as

to permit the percolator proper to be set down onto its base in any relative

orientation with respect to the base, one such connector system being our

CS4/CP7 360° cordless connector system which is the subject of our British

Patent No. 2 285 716.

The above and further features of the present invention are set forth in

the appended claims and will be explained more fully hereinafter with

reference to the accompanying drawings.

Description of the Drawings:

Figure 1 shows a full size plan view of a thick film heating element

embodying the present invention, the final insulation layer of the element

being omitted;

Figure 2 shows how the heating element of Figure 1 appears with its

final insulation layer in place; Figure 3 shows the heating element of Figures 1 and 2 with a power

supply inlet connector and a contact thermostat coupled thereto;

Figure 4 shows a first side elevation view of the arrangement of Figure

3; Figure 5 shows a second side elevation view of the arrangement of

Figure 3;

Figure 6 is an enlarged perspective view of the Figure 3 arrangement;

and

Figure 7 schematically illustrates the arrangement of Figures 3 to 6

mounted in an exemplary percolator appliance.

Detailed Description of the Embodiments:

Referring first to Figure 1, the thick film heating element 1 shown

therein is for a recirculatory-type percolator tea maker and comprises a

substrate 2, a thin stainless steel plate for example, having an

electrically-insulating layer, of glass for example, formed on the underside

thereof, a heating element track pattern 3 formed by printing conductive paste

onto the just-mentioned electrically- insulating layer and firing the printed

paste, and an additional electrically-insulating layer, of glass for example,

overlying the printed conductive track pattern with openings provided in the

additional layer for electrically accessing the track pattern. If desired, the

upper side of the substrate 2 may also be provided with an

electrically-insulating layer, such as of glass. The heating element track pattern 3 in Figure 1 comprises a main

heating element portion 3-1 in the form of a spiral having end terminations 4

and 5, and a further "keep warm" heating element portion 3-2 radially outside

of the main heating element portions 3-1, the "keep warm" heating element

portion 3-2 having one end coupled to the outer termination 4 of the main

heating element portion 3-1 and having its other end coupled to a termination

6 which in turn is coupled to a spaced-apart further terminal portion 7 by

means of an electrically-conductive track portion 8. As is well known, the

heating element portions 3-1 and 3-2 are formed of electrically resistive

material and the terminations 4,5,6 and 7 are formed of an electrically conductive material, silver for example, as is the track portion 8.

Figure 2 shows the additional electrically insulating layer 9 overlying

the heating element track pattern 3 and shows openings 10 provided in the

layer 9 for accessing the terminal portions 4,5,6 and 7. A further opening 11

enables an electrical ground (earth) connection to be made to the substrate 2.

Figures 3 to 6 show the heating element 1 of Figures 1 and 2 having

coupled therewith a CP7 electrical input connector 20 constituting the vessel

mounted part of a CS4/CP7 360° cordless connector system as

aforementioned, it being appreciated that the heating element 1 is intended to

be mounted in a cordless type of vessel which is adapted to be powered when

the vessel is seated on a base having a complementary CS4 electrical output

connector and the CS4 output connector on the base is correctly mated with the CP7 connector on the vessel. The CP7 connector is conventionally

provided with three spade terminals 21, 22 and 23 and, as best shown in

Figure 6, in the arrangement of Figures 3 to 6 respective spring contacts 24

and 25 are affixed to the spade terminals 21 and 23 and are shaped for making

resilient contact with the terminal portions 5 and 7 of the heating element.

The CS4/CP7 360° cordless connector system is commercially available and

will not be described further herein. A similar 360° cordless connector system

which could also be used in the practice of the present invention is available

from Strix Ltd. and is described in WO95/08204.

Additionally coupled to the heating element 1 is a contact thermostat

30 which can for example be as described in our British Patent Application

No. 9807924.7 filed 14 April 1998, the contact thermostat 30 being arranged

with its thermally-sensitive bimetallic switch-actuating element (not shown)

in good heat transfer relationship with the keep-warm track 3-2 of the heating

element and with its spring terminals 31 and 32 in contact with the heating

element terminal portions 4 and 6 respectively.

Figure 7 shows the heating element cum 360° inlet connector and

contact thermostat of Figures 3 to 6 mounted in an exemplary percolator

appliance 40 which comprises a percolator vessel 41 having mounted

therewithin a percolator structure 42 comprising a perforated filter basket 43,

a tubular column 44 and an inverted saucer-shaped or frustoconical member 45 of a diameter substantially equal to that of the spiral main heating element

track and perforated in its upper surface 46.

The CP7 electrical input connector 20 and the contact thermostat 30

can be coupled with the heating element 1 in any convenient manner. The

CP7 input connector 20 could be formed integrally with a carrier for the

contact thermostat 30, for example as described in our British Patent

Application No. 9717144.1 filed 12 August 1997. The spring connections

made between these components and the heating element terminations are

advantageous inter alia because they avoid the cost and trouble of supplying

and fitting separate wires and they readily accommodate manufacturing

tolerances. A similar spring connection could be provided between the earth

(ground) terminal 22 of the input connector 20 and the earthing point 11 on

the heating element.

The contact thermostat 30 is responsive to the temperature of the

keep-warm track 3-2 and serves to short out the keep-warm track so long as its

temperature is below the set operating temperature of the contact thermostat,

which is typically 85 to 95°C. As percolation progresses and the water

temperature overall increases, it being appreciated that only a small volume of

the water is heated by the main percolation heating element track 3-1, so the

contact thermostat eventually operates and opens its contacts thereby

connecting the keep-warm heating element track 3-2 in series with the main

heating element track 3-1. This reduces the total power output of the heating element 1 typically from about 700 watts when only the main track 3-1 is

powered to about 70 watts when both tracks 3-1 and 3-2 connected in series

are powered. This reduced power serves to keep the percolated beverage

warm and serves also to prevent the contact thermostat 30 from resetting.

The position of the contact thermostat 30 close to but not over the

main heating element track 3-1 enables it to serve additionally as a dry boil

protector, that is to say a device to protect the heating element against

overheating as a result of the percolator being switched on without first being

filled with water. The relatively low temperature setting of the thermostat 30

as compared to the typical temperature setting of a more conventional dry boil protector, around 90°C as compared to 150°C, means that the thermostat 30

should respond sufficiently rapidly to heat from the main heating element

track 3-1 conducted by the element substrate to the location of the thermostat

30. As described in British Patent Application No. 9807924.7, the thermostat

30 is provided with a secondary level of protection by virtue of incorporating

a fusible rod of plastics material which is adapted to melt and release an

electrical connection in the event of the sensed heating element temperature

continuing to rise above the temperature at which the thermostat should

normally have disconnected it from its power supply. In the arrangement of

Figures 3 to 6, the thermostat 30 is orientated so that the integral thermal fuse

constituted by the abovementioned fusible rod is close to the main heating

element track 3-1 to ensure that the secondary protection afforded by the fusible rod is sufficiently responsive to ensure that no permanent damage is

suffered by the main heating element track 3-1 m a situation where, for

whatever reason and no matter how unlikely, the thermostat 30 fails to operate

at its normal operating temperature and the heating element continues to be

powered.

Alternatively or additionally a dry boil protector, which could be a

second contact thermostat set to a higher operating temperature, could be

located over the main heating element track 3-1 If such an arrangement were

employed, the arrangement that is descπbed in our Bπtish Patent Application

No. 9717144 1 would be a convement way of mounting the thermostats and the 360° power input connector.

The tight spiral of the mam heating element track 3-1 provides

uniform heat distribution and high power density within a relatively small

area, which is advantageous for use m a percolator, and minimizes stresses

due to uneven heating The close spiral spacing is made possible by virtue of

the provision of the central terminal 5 which ensures that there is only a low

voltage difference between adjacent turns of the track spiral If the spiral

track were turned back upon itself at the centre so that both terminations of

the track were more conveniently located adjacent each other at the outside of

the track, there would be a greater voltage difference between adjacent turns

and the spiral could not be so tightly wound. Furthermore, with a double

spiral arrangement there would unavoidably be a cold spot in the centre of the heating element where the track would have to bend in order to turn back

upon itself. By virtue of the arrangement shown in Figure 1, the central cold

spot unavoidably present by virtue of the provision of track terminal portion 5

is minimized, the terminal portion 4 being only sufficiently large to be reliably

contacted by the spring terminal 24 that is coupled to the CP7 power inlet

connector 20. The compact main heating track 3-1 allows a small and neat

design for the bottom part of the percolator column, and gives good isolation

to the remaining area of the heating element, the heating element substrate

preferably being of stainless steel which has a relatively low thermal

conductivity as compared, say, to copper or brass, so that heat transfer to

liquid in the percolator is substantially only as a result of percolation. This is important since the timing of the percolator operation is dependent upon the

progression of the temperature of the overall body of the liquid to the

operating temperature of the thermostat 30.

Whilst stainless steel is presently preferred as the material of the

heating element substrate, a material having a higher thermal conductivity

could be advantageous in certain circumstances. If the present invention were

to be put into effect using a very thin stainless steel substrate, for example less

than 1.0mm thick, the correspondingly low thermal mass of the heating

element combined with its low thermal conductivity could result in the

heating element self-destructing in a dry boil situation before the contact

thermostat 30 had time to operate, given the reduced thermal transfer sideways through the very thin heating element substrate. In such a case, a

material having a higher thermal conductivity might be advantageous, though

the problem could be overcome by providing a further thermostat in direct

heat transfer relationship with the main track portion 3-1 of the heating

element.

Having thus described the present invention by reference to a specific

embodiment, it is to be appreciated that the described embodiment is

exemplary and that modifications and variations could be made thereto

without departure from the spirit and scope of the present invention. For

example, our British Patent Application No. 9717144.1 discloses a multiple

percolator structure and the present invention could be embodied in such a

structure, there being multiple spiral heating element portions akin to the track

portion 3-1 hereinbefore described and the CP7 inlet connector carrying

appropriate spring terminals for contacting the multiple heating element

portions and supplying power thereto. In such an arrangement the multiple

main heating element portions could be connected in parallel or in series with

one another by means of the connections provided on the CP7 inlet connector,

and either there could be a single keep-warm track section serving all of the

multiple main heating element track portions and a single thermostat

associated therewith or each main heating element track portion could have

associated therewith its own keep-warm track portion and its own control

thermostat. The high speed percolation promised by the invention of our British Patent Application No. 9717144.1 could thus be achieved in the

practice of the present invention.

Claims

CLAIMS:

1. A thick film electric heating element for a percolator, the heating

element comprising a main heating element track for association with a

percolator structure and a keep-warm heating element track outside of the

region of the heating element occupied by the main heating element track, the

main heating element track having a spiral form with terminal portions at the

centre of the spiral and at the outer end thereof and the keep-warm track

having one end connected to the terminal at the outer end of the main heating

element track and having its other end connected to an adjacent terminal, the arrangement enabling a temperature sensitive device connected between the

terminal ends of the keep-warm track to determine the percolation time of the

percolator by virtue of being responsive to the heating element temperature

outside of said region to connect the keep-warm heating element track in

series with the main heating element track when said temperature rises to a

predetermined level .

2. A thick film electric heating element as claimed in claim 1 wherein the

arrangement of the keep-warm heating element track is such as to enable said

temperatures sensitive device to be responsive to the heating element

temperature at a location traversed by the keep-warm heating element track.

3. A thick film heating element as claimed m claim 1 or 2 wherein the

keep-warm heating element track surrounds the main heating element track.

4. A thick film heating element as claimed in any preceding claim

wherein the mam heating element track occupies only about a quarter of the

area of the heating element.

5. A thick film heating element as claimed in claim 4 wherein the heating

element is a circular disc having a diameter of the order of 100mm and the

main heating element track occupies a central circular region of the disc

havmg a diameter of the order of 50mm.

6. A thick film heating element as claimed in any of the preceding claims

wherein the power output of the seπes connected mam and keep-warm tracks

is about one-tenth of the power output of the mam heating element track when

the keep-warm track is out of circuit.

7. A thick film heating element as claimed in claim 6 wherein the mam

heating element track is arranged to deliver about 700 watts when the

keep-warm heating element track is out of circuit, and the connected main and

keep-warm tracks are arranged to deliver about 70 watts.

8. A thick film heating element substantially as herein described with

reference to the accompanying drawings.

9. A thick film heating element as claimed in any of the preceding claims

in combination with a temperature sensitive device as aforesaid connected

between the terminal ends of the keep-warm track.

10. A combination as claimed in claim 9 wherein the temperature sensitive

device comprises a contact thermostat.

11. A combination as claimed in claim 10 wherein said contact thermostat

incorporates a bimetallic device arranged to open a pair of switch contacts

when the bimetallic device responds to a temperature exceeding a set level.

12. A combination as claimed in claim 8 or 10 or 11 wherein said

temperature sensitive device has external spring contacts held in contact with

the terminal ends of the keep-warm heating element track.

13. A combination as claimed in claim 9 or 10 or 11 or 12 wherein said

temperature sensitive device incorporates a secondary protection arrangement

operable at a temperature higher than the normal operating temperature of the

device.

14. A combination as claimed in claim 13 wherein said secondary

protection arrangement is arranged in said temperature sensitive device so as

to be responsive to the temperature of the heating element at a part thereof

which is closely adjacent to the main heating element track.

15. A heating element as claimed in any of claims 1 to 8, or a combination

as claimed in any of claims 9 to 14, in combination with a power supply input

connector having terminals coupled to the terminal at the centre of the main

heating element track spiral and to one of the keep-warm heating element

terminals.

16. A combination as claimed in claim 15 wherein said power supply

input connector has external spring terminals held in contact with the

respective terminals of the heating element.

17. A combination as claimed in claim 15 or 16 wherein the power supply

input connector is a cordless appliance connector.

18. A combination as claimed in claim 17 wherein the power supply input

connector is a 360° connector.

19. A combination as claimed in any of claims 15 to 18 and substantially

as herein described with reference to the accompanying drawings.

20. A percolator incorporating a heating element as claimed in any of

claims 1 to 8 or a combination as claimed in any of claims 9 to 19.

21. A thick film heating element for a percolator, the heating element

having a main frack occupying only about a quarter of the area of the heating

element and a keep-warm frack, the keep-warm track being adapted to be

connected in series with the main frack so as to reduce the power output of the heating element to about a tenth of its power output when the keep-warm

frack is disconnected.