GB2217629A

GB2217629A - Pressure cooker

Info

Publication number: GB2217629A
Application number: GB8800979A
Authority: GB
Inventors: Harold Robert Holt
Original assignee: MERWOOD Ltd
Current assignee: MERWOOD Ltd
Priority date: 1988-01-16
Filing date: 1988-01-16
Publication date: 1989-11-01
Also published as: GB8800979D0

Abstract

A pressure cooker 1 has a cooking container 8 in which is disposed an electric element 4. The element 4 comprises inner and outer concentric conductors 13, 14 which are separated by a gap and connected to opposite terminals of a power supply. The outer conductor 14 has a plurality of water inlets 16. In use, water passes through the inlets 16 to contact the conductors 13, 14 and thereby complete the electrical circuit. The liquid itself provides an electrical resistance path between the electrodes and as energy is dissipated in this path the water is turned to steam. The supply of current to the element is controlled by a switch 52 which is actuated according to the pressure in the container. <IMAGE>

Description

PRESSURE COOKER This invention relates to pressure cookers.

The use of pressure cookers as a quick, efficient, energy saving means of cooking, has been known for some time. However, known pressure cookers require a heating source external to the main body of the appliance.

We aim to improve upon this by providing a pressure cooker which does not require an external heating source.

According to one aspect of the present invention, there is provided a pressure cooker which is electrically powered by means of an element disposed within the pressure cooker.

Preferably, the element comprises two conductors separated by a gap. The conductors may comprise two concentrically disposed electrically conductive tubes of different radii which are not in direct electrical contact with one another. Means is provided for allowing water to contact both conductors simultaneously. The water completes the electrical circuit between the two conductors to provide electrical resistance heating.

Electricity supply terminals may be provided in a lid of the cooker which terminals automatically make electrical contact with the element, when the lid is secured in a position in which it closes the contact.

Preferably the element is removeable for ease of servicing.

There may be a plurality of elements as aforesaid.

The pressure cooker may include a diaphragm which is provided within the pressure cooker to regulate steam pressure and flexes under steam pressure, and regulation means which respond to flexure of the diaphragm. The diaphragm may, on flexing a predetermined distance, cause actuation of a microswitch which controls a supply of electricity to the element.

The pressure cooker may include a means for adjusting steam pressure within the pressure cooker.

Preferably, the pressure cooker includes a pressure adjuster which is operative to move said microswitch closer to or further away from the diaphragm, so that said predetermined distance is reduced or increased respectively.

The pressure cooker may be sealed by means of a sealing ring which is fitted to a lid of the cooker.

Preferably the sealing ring is compressed by vertical forces which cause the sealing ring to expand horizontally to engage sealingly a side wall of the cooker. The vertical forces may be transmitted to the sealing ring by means of a post which is mounted on the lid, which post is urged vertically downwards by a cam mechanism provided on the lid. The sealing ring may be inhibited from expanding radially inward so that radially outward expansion is facilitated.

Preferably the pressure cooker includes filters for filtering water in the cooker.

According to a second aspect of the present invention there is provided an electrical resistance heating device comprising two electrodes, defining therebetween a gap, filled with a liquid to be heated, such that the liquid itself provides an electrical resistance path between the electrodes, and in use, heat is generated in said resistance path, thereby heating said liquid.

According to a further aspect of the present invention there is provided a device for regulating pressure within a pressure vessel, the device comprising a diaphragm which flexes under steam pressure within the vessel, and pressure regulating means which responds to flexure of the diaphragm to regulate pressure within the vessel.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: Figure 1 is a longitudinal cross-section through a pressure cooker; Figure 2 is a transverse section through an element of the pressure cooker taken along the line Y-Y of Figure 1; Figure 3 is a transverse section through the element, taken along the line X-X of Figure 1; Figure 4 is a sectional view of an alternative pressure regulating device, and Figure 5 shows a locking catch in front view.

The illustrated pressure cooker 1 comprises an outer casing 2 within which an inner container 3 is disposed. An element 4 is provided within the inner container 3. A lid assembly 5 having a top cover 57 engages the inner container 3 and the element 4, to seal the inner container 3, as will be described in more detail below.

The outer casing is made of a strong, durable, supportive shell, which is filled with foam 42 or other thermally insulating material, which acts as a lagging for the inner container 3.

The inner container 3 has a wall 7 which is both electrically and thermally non-conductive. A trivet 9 is provided at the bottom of the inner container, which trivet 9 supports two cooking containers 8, disposed one above the other, and also allows fluid to pass through it into filters 10, which may remove dust, portions of food, or any other debris which may be detrimental to the efficient working of the element 4. The element 4 passes through the centres of the containers 8, which provide horizontal support for the element. At its lower end, the element rests upon a support plate 12 provided on the inner container 3. In order to remove the element 4 from the inner container, the lid assembly 5 is removed, and the element is lifted upwards through the centres of the cooking containers 8.

It may be seen from Figure 1 that the inner wall 6 of the outer casing 2 tapers, so that the diameter of the cavity defined by the inner wall increases towards the lid end of the appliance. The inner container 3 is similarly shaped. This allows the cooking containers 8 to be easily removed from the inner container 3 in order to fill with food, remove cooked food or to clean. The inner container 3 (including the element 4) is removeable from the outer casing 2 for ease of cleaning and/or servicing.

The element 4 comprises two concentric tubular conductors 13 and 14, which define an annular gap 15 therebetween. Alternatively, the element may comprise two flat electrodes separated by a gap.

The inner conductor 13 is connected in use to the neutral terminal of a power supply, and the outer conductor 14 to the live terminal (or vice versa).

At the base of the element 4, the outer conductor 14 is provided with one or a plurality of water inlets.

In the illustrated embodiment, four water inlets 16, disposed at 900 intervals, are provided. These water inlets allow water to pass into the annular gap 15 and to contact both the inner and outer conductors 13, 14. This water provides an electrical resistance path between the electrical conductors 13 and 14 and accordingly, electrical current may pass through the water, between the live and neutral terminals of the power supply.

As will be described in more detail below, the electrical current provides a resistance heating effect, which causes the production of steam in the annular gap 15 and thence a rise in pressure within the inner container 3.

The outside of the element 4 may be provided with a cover 17 which affords protection and electrical insulation.

At its upper end, the element 4 provides two upwardly extending projections 19 and 20 of the outer and inner conductors 14 and 13 respectively, which projections make electrical contact, when the lid assembly 5 is in place, with resiliently flexible connectors 21 and 22 present in the lid assembly 5.

The lid assembly 5 has a locating pin 23 which engages with the element 4 in order to centralize the lid assembly and element. The locating pin 23 has a groove 24 cut into it, within which an end of the flexible connector 22 is disposed, for contact with the projection 20. The flexible connectors 21 and 22 are connected respectively to the neutral and live terminals of the power supply. When the lid assembly 5 is placed correctly in position a safety microswitch (not shown) is automatically actuated which allows power to flow to a manually actuable power supply switch (not shown). This manually actuable switch is switchable to supply power to microswitch 50 which is mounted on the lid assembly 5 by means of a bracket (not shown). A manually actuable switch is also provided which allows power to flow to the safety microswitch.

A circular body 29 is disposed at the bottom of the lid assembly 5, and carries upstanding posts 28 at the top of which pins 27 are provided. The top cover 57 is moveable with respect to the circular body 29 and parts carried thereon. Such parts include an abutment plate 56 which bears firmly against the top of the inner container 3.

The lid assembly 5 is also provided with two locking catches 90 at opposing sides of the lid assembly.

Only one of these is shown in Figure 1 for clarity, and is shown in Figure 5 in more detail.

The locking catch 90 comprises two lock release arms 33, provided with extensions 91 which are pivotally mounted at 92 on a part (not shown) which is in fixed relationship with the circular body 29. The extensions 91 are resiliently biased, by the force of a spring 93, so that jaws 94 are urged together. The jaws 94 are so shaped as to engage, when the lid assembly is placed in position, a triangular projection 95 provided on the outer case 2 of the pressure cooker. Release of the lid assembly is accomplished by squeezing together the release arms 33 so that the jaws 94 are disengaged from the projections 95.

A safety lock 32 is provided so that the lid assembly cannot be released when the appliance is switched on.

A locking lever 25 with handle is pivotally mounted on the pins 27, and is provided with cam plates 18. Upon pivoting the lever 25 from the illustrated upright position to a position in which it is generally flat on top of the top cover 57, the cam plates 18 bear on the adjacent top surface of the top cover 57, thereby to urge the top cover 57 downwardly with respect to the lever 25. This has the effect of compressing a circular, resilient rubber seal 26 under a rigid ring 30 mounted on posts 31 which are secured to the top cover 57. Upon being so compressed, the seal 26 is urged radially outwards, to seal against the side wall of the inner container 3. As may be seen in Figure 1, the seal 26 is located in an annular recess in the body 29, which prevents radically inward expansion of the seal 26.

When the locking lever 25 is pivoted as described above, a connector pin 86 attached thereto moves upwards.

Accordingly, an actuator pin 82 of the safety lock 32, which is attached to the pin 86 and which passes through the top cover 57 moves upwards. The actuator pin 82 is attached to a pair of pivotable projections 84 at 83 (only one projection 84 may be seen in Figure 1). When the actuator pin 82 moves upwards, the projections 84 pivot anti-clockwise about a pivot point 81. This causes the projections 84 of the safety lock 32 to move inbetween the lock release arms 33. In this position the projections 84 impede the squeezing together of the lock release arms 33. Accordingly, when the locking lever 25 is flat on top of the lid 5, the lid assembly cannot be removed.

Only one safety lock 32 may be provided as shown, or a respective safety lock 32 may be provided for each locking catch 90.

When the locking lever 25 is pivoted as described above, a projection 78 thereof engages with the microswitch 50 to actuate it.

The pressure cooker 1 is provided with a pressure sensing mechanism, which utilizes a flexible diaphragm 40 which is in communication with the inner container 3 by means of perforations (not shown) provided in plate 100.

The diaphragm 40 is in contact with a plate 51 which is slidable upon, and in the direction of, four vertical posts 55, which are disposed at 900 intervals to each other, and are infixed relationship with the circular body. Upon sliding on the vertical posts 55, the plate 51 may engage a microswitch 52 which is fixed by means of a bracket 58 to a plate 59.

When the pressure rises, the diaphragm 40 pushes the plate 51 upwards. The plate 51 moves towards the microswitch 52, and upon reaching it, actuates it. This has the effect of switching off electrical current to the element 4, as a result of which, pressure in the inner container falls. As the pressure falls, the diaphragm 40 relaxes and the plate 51 moves away from the microswitch 52. Accordingly, the microswitch 52 is actuated again and the current may again flow through the element 4.

The lid assembly 5 is also provided with a pressure and/or temperature response safety valve 72 of conventional design. The valve vents the inner container 3, via a pipe which passes through the lid to the atmosphere. An end of the pipe open to the atmosphere, may be directed into a container of cool water provided as a component of the body of the pressure cooker, or more simply the pipe may be directed to any water container external to the pressure cooker.

The valve 72 may be actuated either when the normal pressure sensing mechanism fails, and allows the pressure within the inner container 3 to rise above a predetermined safe level or if steam in the inner container becomes superheated and causes the temperature therein to rise above a predetermined safe level.

A manual pressure release valve (not shown) is also provided. This valve is connected by a tube to a part of the pipe which passes through the lid assembly to the atmosphere.

The pressure of steam in the inner container 3 may be varied by means of a pressure adjuster 70. The pressure adjuster 70 consists of a screw 60 which engages a nut 62 secured in the lid assembly 5. At its lower end the screw 60 is fixed into the plate 59. When the pressure adjuster 70 is screwed downwards, the plate 59 moves downwards, which movement results in the microswitch 52 being brought closer to the diaphragm 40.

Consequently, a lower pressure will be required to flex the diaphragm a sufficient amount to cause plate 51 to engage the microswitch 52. Conversely, when the pressure adjuster 70 is screwed upwards, the plate 59 and microswitch 52 are moved further away from the diaphragm 40. A mechanical stop is provided (not shown) which stop limits the extent of travel of the plate 59.

A pressure indicator 71 is attached to the plate 59 and moves therewith. A graduated scale 73 is provided on the pressure indicator 71 which scale gives an indication of the vertical position of the plate 59. The scale may be calibrated in order to give a direct reading of the actual pressure at which the appliance is being operated. As an alternative pressure indicator a dial may be provided which is suitably linked to the pressure sensing apparatus of the appliance.

The pressure cooker may be operated as follows: The cooking containers 8 are filled with the food to be cooked and placed in the inner container 3. The element 4 is placed through the centres of the cooking containers 8 which provide horizontal support for it. A small amount of water is poured into the inner container.

The water passes through the trivet 9, enters the filters 10, and settles at the bottom of the inner container 3.

The water passes through the inlets 16 and into the annular gap 15 of the element 4, thereby providing electrical contact between the inner and outer conductors 13 and 14.

The lid assembly 5 is placed in position on top of the container 3, ensuring the locating pin 23 engages with the element 4. In this position, the catches 90 snap-engage, the safety microswitch (not shown) is actuated automatically, and the flexible connectors 21 and 22 make electrical contact with the upwardly extending projections 19 and 20 respectively. The manually actuable switch is turned to the ON position.

The pressure at which the unit is to function is selected by means of the pressure adjuster. 70, which is screwed either up or down to increase or decrease the operating pressure of the appliance. The cooking time is then selected on a timer.

The locking lever and handle 25 is pivoted through about 900 until it lies substantially flat on top of the top cover 57. This causes the seal 26 to bear firmly against the inner container 3. It also causes the automatic actuation of the safety lock 32 and the microswitch 50.

Accordingly, the electrical circuit between the live and neutral terminals of the power supply, including the electrical resistance path provided by the water in the annular gap 15 between the electrodes 13, 14, is completed. In view of the relatively small amount of water in the annular gap 15, and the relatively low electrical resistance of the water, the water is heated very rapidly, and indeed virtually instantaneously, to produce steam within the gap 15, and consequently within the inner container 3. As more steam is produced, the pressure within the container 3 rises, and the food cooks in the pressurized steam.

The flexible diaphragm 40 communicates with the inner container 3, so that as the steam pressure increases, the diaphragm flexes against the plate 51, which moves upwards on the vertical posts 55 towards microswitch 52. Eventually when the operating pressure is reached, the diaphragm pushes the plate 51 against the microswitch 52, to switch off the flow of current to the element 4, and in turn steam production ceases. An indicator light (not shown) is automatically lit, to indicate to a user that the selected pressure has been attained. The pressure -in the inner container will now fall and accordingly the diaphragm 40 relaxes, plate 51 disengages from the microswitch 52, power to the element returns and steam production restarts.This series of events continues throughout the operation of the appliance, so that a generally constant steam pressure is maintained within the inner container.

Should the diaphragm, or any other part of the pressure sensing mechanism, fail, steam will be continuously produced and pressure in the inner container will continue to rise. The safety valve 72 will vent the inner container 3 to the atmosphere, when a maximally allowed pressure is reached, thus ensuring that the pressure in the inner container does not rise to an uncontrolled unsafe level.

When the food has been cooked for a long enough period of time, the timer will indicate this by a visible and/or audible alarm to the user, who will then switch off the manually actuated power supply switch to switch off power to the pressure cooker. Alternatively, the timer may be operative to switch off the power automatically at the end of the cooking time.

The pressure in the inner container 3 must be released slowly so as not to cause any sudden changes in pressure which may be unsafe. To this end, the manual pressure release valve is provided. As the pressurized steam is released, it may be directed into a container of water to condense the steam, and accordingly prevent steam filling a kitchen in which the pressure cooker is being used. The container of water may be a sink, into which steam is directed by a flexible hose, the end of which may be secured in the sink (or other container) by, for example, a suction pad.

As indicated above, the body of the pressure cooker may incorporate a reservoir of water through which steam released from the inner container 3 is automatically directed.

The locking lever 25 may now be released, thus releasing the rubber seal 26. A mechanical stop may be provided to prevent release of the locking lever when a substantial pressure is present in the inner container.

The lid assembly 5 and the cooking containers 8 may then be removed.

As an alternative to the provision of water inlets 16 in the element 4, as described above, water may be held in a reservoir above the element, and means provided for allowing water to be gravity fed through the orifice 100 (Figure 2), when required. In this case, instead of water inlets 16, water inlets may be provided in the inner conductor 13 so that water may contact both conductors of the element as before.

It may be desirable to provide a means of monitoring the current flowing between the conductors of the element and providing current protection means which switch off current to the element when the current flowing through is too high. It will be appreciated that the current flowing through the conductors of the element may give an indication of the amount of water present therebetween and accordingly this information may be used to control the amount of water fed through the orifice 100.

One or a plurality of non-centralised heating elements may be provided, in which case, the shape and disposition of the cooking containers will be altered accordingly.

An alternative pressure regulating apparatus which may be adapted to replace the diaphragm etc of Figure 1, is shown in Figure 4. Steam enters the pressure regulator 109 via steam inlet passage 112 and impinges on the diaphragm 110. As the diaphragm is urged upwards against a resilient force provided by a spring 111, a plunger 117 abutting against the diaphragm is moved upwards. In turn, this causes a striker plate 115 to move upwards towards a microswitch (not shown) attached to a lower surface of a pressure adjustment plate 118. A thimble 116 attached to the striker plate will eventually engage the microswitch in a similar manner to the aforementioned pressure regulating apparatus of Figure 1. A purging outlet 113 is provided which ensures the efficient working of the diaphragm.

It will be appreciated that the aforementioned pressure regulating apparatus, need not be disposed on a longitudinal axis of the appliance and that it may in fact be more convenient otherwise disposed.

In an applicable alternative method of sealing the pressure cooker, the arrangement is modified such that a seal such as 26 bears against an upper face of the inner container 3, instead of or as well as the side walls thereof.

As an alternative to the mechanically operated pressure regulating system, an electric pressure transducer ' may be provided. This transducer receives information about steam pressure and initiates the regulation thereof.

In another alternative, an electronic pressure adjustment means may be provided.

The pressure cooker may be provided with a valve through which steam may be tapped off. It will be appreciated that in this case, the pressure cooker may be used as a steam generator, and steam may be dispersed through a nozzle for cooking foods, heating liquids, etc.

A modification of the manual pressure release valve may be sufficient to provide this utility.

The aforementioned embodiments may be applicable to relatively small domestic cookers or to larger cookers for use in the catering industry. It may be advantageous to provide the larger cookers with castors for ease of transport etc. For ease of use, handles may be provided to aid the release of the lid. Also, a hinged bracket may be provided on, for example, one side of the pressure cooker to provide a resting place for the lid when it is not in its normal position. Alternatively, a hinged lid may be provided with a suitable locking mechanism provided opposite the hinge.

The pressure cooker may be used to cook vegetables or any food which may be cooked by steam, for example, poached eggs.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification and/or drawings, or to any novel one, or any novel combination, of the steps of any method or process disclosed herein.

Claims

CLAIMS:

1. A pressure cooker which is electrically powered by means of an element disposed within the pressure cooker.

2. A pressure cooker according to Claim 1, wherein the element comprises two conductors separated by a gap.

3. A pressure cooker according to Claim 1 or 2, wherein the conductors comprise two concentrically disposed electrically conductive tubes of different radii which are not in direct electrical contact with one another.

4. A pressure cooker according to Claim 1, 2 or 3, wherein means is provided for allowing water to contact both conductors simultaneously.

5. A.pressure cooker according to Claim 4, wherein water completes the electrical circuit between the two conductors to provide electrical resistance heating.

6. A pressure cooker according to any of the preceding claims, wherein electricity supply terminals are provided in a lid of the cooker, which terminals automatically make electrical contact with the element, when the lid is secured in a position in which it closes the cooker.

7. A pressure cooker according to any of the preceding claims, wherein the element is removeable for ease of servicing.

8. A pressure cooker according to any of the preceding claims, in which there are a plurality of elements as aforesaid.

9. A pressure cooker according to any of the preceding claims, including a diaphragm which is provided within the pressure cooker and flexes under steam pressure, and regulation means which responds to flexure of the diaphragm to regulate the steam pressure.

10. A pressure cooker according to Claim 9, in which the diaphragm, on flexing a predetermined distance, causes actuation of a microswitch which controls a supply of electricity to the element.

11. A pressure cooker according to any of the preceding claims, including means for adjusting steam pressure within the pressure cooker.

12. A pressure cooker according to Claims 10 and 11, including a pressure adjuster which is operative to move said microswitch closer to or further away from the diaphragm, so that said predetermined distance is reduced or increased respectively.

13. A pressure cooker according to any of the preceding claims, wherein the pressure cooker is sealed by means of a sealing ring which is fitted to a lid of the cooker.

14. A pressure cooker according to Claim 13, wherein in use, the sealing ring is compressed by vertical forces which cause the sealing ring to expand horizontally, to engage sealingly a side wall of the cooker.

15. A pressure cooker according to Claim 14, wherein the vertical forces are transmitted to the sealing ring by means of a post which is mounted on the lid, which post is urged vertically downwards by a cam mechanism provided on the lid.

16. A pressure cooker according to Claim 14 or 15, wherein the sealing ring is inhibited from expanding radially inward so that radially outward expansion is facilitated.

17. A pressure cooker according to any of the preceding claims, including filters for filtering water in the cooker.

18. A pressure cooker substantially as hereinbefore described with reference to the accompanying drawings.

19. An electrical resistance heating device comprising two electrodes, defining therebetween a gap, filled with a liquid to be heated, such that the liquid itself provides an electrical resistance path between the electrodes, and in use, heat is generated in said resistance path, thereby heating said liquid.

20. A device for regulating pressure within a pressure vessel, the device comprising a diaphragm which flexes under pressure within the vessel, and pressure regulating means which responds to flexure of the diaphragm to regulate pressure within the vessel.

Amendments to the claims have been filed as follows 1. A pressure cooker which is electrically powered by means of an element disposed within the pressure cooker.

3. A pressure cooker according to Claim 1 or 2, wherein the. conductors comprise two concentrically disposed electrically conductive tubes of different radii which are not in direct electrical contact with one another.

5. A. pressure cooker according to Claim 4, wherein water completes the electrical circuit between the two conductors to provide electrical resistance heating.

20. A device according to Claim 19, wherein the electrodes comprise two concentrically disposed electrically conductive tubes.

21. A device according to Claim 20, wherein the tubes are substantially the same length.

22. A device according to Claim 20 or 21, wherein at one end of the outer one of the electrodes, there is provided a water inlet.

23. A device according to Claim 22, wherein at the other end of the electrodes, each conductive tube is adapted to make electrical contact with a respective terminal of a power supply.