GB2047117A - Pressure cookers - Google Patents

Abstract

In pressure cookers which include an electrical heater, the output of the heater can be adjusted by control means 23. On initial heating of the pressure cooker to bring the chamber up to cooking temperature adjustment of the control means causes switching on of a heater switch 28 and closure of a pressure release valve 14. When the required pressure is reached the control means 23 can be adjusted to a lower output of the heater and a timer 40 pre-set for a predetermined time period. The heater switch remains on and the pressure release valve remains closed until the end of the predetermined period when the pressure release valve 14 is automatically opened and the heater switched off. <IMAGE>

Description

SPECIFICATION Pressure cookers The present invention relates to pressure cookers, particularly to pressure cookers for use for domestic cooking. With conventional pressure cookers it is necessary to place the cooker and its contents on an external source of heat (e.g. a gas or electric cooking stove) until the water boils which expels air and steam through the valve. The source of heat must then be adjusted so that the pressure is maintained relatively constant during the cooking period. It is necessary to time the cooking period and at the end of the timed period the pressure in the vessel is reduced to atmospheric pressure (e.g. by opening the pressure valve or by first cooking the cooker with water) and the supply of heat is terminated, e.g. by removing the cooker from the heat source or switching off the heat source.

According to the present invention there is provided a pressure cooker vessel comprising a cooking chamber, an electrical heater for heating the contents of the chamber, a switch for the heater, a pressure release valve adapted to close the chamber, control means for adjusting the output of the heater, said control means including switch means adapted to actuate an operating member to close the pressure release valve and to switch on the heater switch when the control means are adjusted for a first output, a timer and means associated therewith adapted to actuate the operating member to retain the pressure release valve in the closed position and the heater switch in the on position when the control means are adjusted for a second output lower than the first, said timer and associated means being adapted to actuate the operating means to open the pressure release valve and to switch off the heater switch after a predetermined time period.

The pressure cooker of the present invention enables the operator to control the cooking cycle by the operation of simple interconnected means. Adjustment of the control means of the heater for a high output (e.g. the maximum output of the heater) enables the contents of the cooker to be heated in a sealed chamber so as to bring the contents up to pressure. The pressure may be determined by the pressure relief valve being biased to the closed position. This biasing can take the form of weight as in pressure valves of conventional pressure cookers.

Suitable choice of weight will predetermine the pressure within the vessel. If this pressure is exceeded, the excess pressure will raise the weight and steam will issue from the valve. When it is desired to start the cooking under pressure, e.g. when steam is seen issuing from the pressure relief valve or when the required pressure is shown on a pressure indicator, the control means can be adjusted to a lower output which is still capable of maintaining the chamber at a cooking temperature e.g. the heater is regulated by the control means so that the heat input to the cooking chamber is reduced whilst maintaining the chamber at a cooking temperature of above 100"C. Operation of the timer (before or after this adjustment of the control means) causes the cooking cycle to be carried out automatically while the pressure relief valve remains closed.At the end of the cooking cycle the vessel is automatically depressurised by the opening of the pressure relief valve and the heating of the pressure chamber terminated by the switching off of the heater switch.

The pressure cooker can be controlled in an efficient and yet simple manner by the operation of the control means (for regulating the output of the heater) and the timer (for setting the cooking period.

These operations are interconnected since there is a common operating member which can control the operation of the heater switch and the pressure relief valve. Preferably the operating member is adapted to move in a single plane between a first position where it is adapted to actuate the heater switch to the off position and the pressure relief valve to the open position and a second position where it is adapted to actuate the heater switch to the on position and the pressure relief valve to the closed position. The operating member can be in the form of a plate adapted to slide between the first and second positions. The output of the heater is controllable by the control means which can adjust a regulator, e.g. a thermostat having thermostat probes incorporated in the cooker or an energy regulator thermostat.On adjustment of the control means for the first high output the heater can, for example, provide its maximum output (e.g. the heater is activated continuously) so that the cooker is brought up to pressure as quickly as possible. When pressure is seen to be reached the regulator can be set at a lower temperature chosen, for example, by observing a pressure indicator and setting the regulator to give a specified pressure as shown by the indicator.

At this lower temperature the power to the heater is alternatively cut-off and restored under the control of the regulator (e.g. thermostat or energy regulator) while the heater switch is in the on-position.

At the end of the predetermined cooking period the timer actuates the operating member which opens the pressure relief valve and terminates the supply of heat to the chamber. Preferably the timer also includes means adapted to give an audible and/or visible signal at the end of the cooking period.

If desired control means can be included for terminating the supply of heat independently of the opening of the pressure relief valve. Also means can be incorporated for controlling the actuation of the operating member independently of the switch means.

A pressure cooker in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a side elevation of a pressure cooker incorporating the present invention.

Figure2 is a part cross-sectional side elevation of the cooker of Figure 1 as viewed in direction Il-Il of Figure 1.

Figure 3 is a plan view, viewed from above, of the pressure cooker of Figure 2.

Figure 4 is a diagrammatic representation of the sequence of operations during use of the pressure cooker of Figures 1-3.

Figure 5 is a front elevation of an alternative time/temperature pressure release assembly.

Figure 6 is a cross-sectional view of the time/ temperature pressure release assembly of Figure 5 as viewed in direction VI-VI of Figure 5.

Figure 7 is a perspective view of part of the mechanism of the assembly of Figure 5.

Figure 8 is a diagrammatic representation of the sequence of operations during use of the embodiment of Figures 5 to 7.

As shown in Figures 1 to 4 of the drawings a pressure cooker comprises a main body portion 10 and a lid portion 11 which are arranged to clamp together when suitably ailigned to form an internal chamber. The body portion 10 and the lid portion 11 have carrying and lid closure handles 12, 12a and 13, 13a.

A pressure relief valve 14 is provided on the lid 11.

The valve is of known type having a port through the lid 11 which is adapted to be closed by needle, the upper end of which is attached to a lower weight 15, on which is carried two further weights 16 and 17.

The weights 15,16 and 17 provide biasing means for keeping the port closed and the amount of biasing can be adjusted by removing or altering one or more of the weights. A knob 18 is attached to the weights to aid in their removal.

Removably attached to the side of the body portion is a time/temperature pressure release assembly, indicated generally be reference number 19, which is explained in greater detail below.

Attached to the lid 11 is a depressurisation linkage assembly generally indicated by reference number 20, which is also explained in greater detail below.

An electric heating element (not shown) attached to the bottom of the base portion 10 has element probes 22 adapted to make contact with corresponding sockets in a variable thermostat control 23 in the time/temperature pressure release assembly 19. The variable thermostat control 23 has a thermostat probe (not shown) adapted to enter the bottom of the base portion 10, between the probes 22 so as to monitor the temperature within the pressure cooker.

The temperature setting of the variable thermostat control 23 is adapted to be varied by means of a circular rotatable thermostat temperature dial 24 having an upstanding rim 25. Mounted on the interior surface of the rim 25 are two sprung plungers, one of which, 26, is shown.

Power is adapted to be supplied to the variable thermostat control 23 via a lead 27. The supply of electricity is controlled by an on/off microswitch 28 mounted within the housing 29 of the timer-pressure release assembly 19. Mounted on the outside of the housing 29 are neon indicator lamps 30, 31 which are connected so as to indicate whether the power is on or off.

The movable contact 32 of the microswitch 28 is adapted to be closed by vertical movement of a metal slider 33 mounted within the housing 29 in such a manner that is can be moved vertically up and down as more fully explained below. The slider 33 has a lower vertical limb 34, a horizontal limb 35 and an upper vertical limb 36. Upward movement of the slider causes the horizontal limb 35 to push against the contact 32 and hence close the microswitch while downward movement of the slider enables the contact 32 to open.

Mounted on top of the upper vertical limb 36 of the slider 33, externally of the housing 29, is a knob 37.

The lower vertical limb 34 of the slider 33 has an opening 38 having a cam ear 39 in its wall.

A clockwork timer 40 is adapted to drive a spindle 41 within a housing 42 of the timer-pressure release assembly 19. The housing 42 contains a window 43 to enable the operator to see the time scale on the timer dial housing 44. Mounted on the spindle 41 is a cam 45 located in the opening 38 of the slider 33. The cam surface of the cam 45 bears against the cam ear 39 of the opening 38. The spindle 41 may be rotated, and hence the timer pre-set, by means of the knob 46.

A rotatable trigger 47 is pivotally mounted below the timer 40. The trigger 47 carries three permanently joined cams 48,49, 50. Cam 48 is a "thermostat operated cam" and is adapted to be contacted by the sprung plungers, e.g. 26, of the thermostat. Cam 49 is a "timer operated cam" and it is adapted to be contacted by a cam surface within the timer dial housing 44. Cam 50 is a "slider actuating cam".

Rotation of the trigger 47 by means of cams 48 or 49 causes rotation of the cam 50 which is adapted to act upon the slider 33, as more fully explained below.

The depressurisation linkage assembly 20 has a housing 51. Housing 51 has a circular opening for the weights of the pressure relief valve and also interconnected elongated openings 53 to enable steam from the pressure relief valve to be directed away from the direction of timer pressure release assembly 19, i.e. away from the operator. The housing 51 is attached to the lid 11 of the pressure cooker. Within the housing 51 is an elongated metal lever 54 pivoted about a point 55 between its ends.

The end 56 of the lever 54 is slightly upturned, below the pressure relief valve 14, so that when end 56 is raised vertically the weights of the valve 14 are raised so opening the valve. The other end of the lever 54 passes through an opening in the housing 51 and carries a turn button 57. The lever 54 also carries a knob 58, which in the position indicated in Figure 2 is in intimate contact with knob 37 of the timer-pressure release assembly 19 under the biasing of a spring 59. However, the turn button 57 may be rotated so that the knob 58 is clear of the knob 37.

In the embodiment shown in the drawings, the lid 11 is provided with an emergency pressure relief valve 60.

The operation of the pressure cooker of Figures 1 to 3 will now be described with particular reference to Figure 4. The base and lid portions 10,11 of the pressure cooker are connected to the timer-pressure release assembly 19 by inserting the element probes 22 into the corresponding sockets in the body of the timer-pressure release assembly 19. The food to be cooked is placed in the chamber and the lid 11 replaced on the body 10 with the weights of the pressure relief valve 14 in the raised position. The mechanism is now in the position illustrated in Figure 4(a). Power is switched on and the thermostat temperature dial 24 is turned to its maximum setting. Turning the dial 24 causes one of the sprung plungers 26 to contact the thermostat operated cam 48 of the trigger 47.This in turn causes rotation of the trigger so that the slider actuating cam 50 contacts and vertically raises the slider 33. The raised horizontal limb 35 of the slider closes the contact 32 of the microswitch 28 so completing the circuit sothatthe heating element produces a high output to rapidly heat the contents ofthe chamber.

As the same time the raising of the slider causes the knob 37 on its upper vertical limb 36 to push knob 58 on lever 54 and hence causes lever 54 to pivot so that end 56 is lowered. Lowering of end 56 causes the weights of the pressure relief valve 14 to be lowered so closing the valve. The mechanism is now in the position illustrated in Figure 4(b).

When the required pressure within the cooker is reached, as indicated by steam issuing from the relief valve 14, the operator adjusts the thermostat temperature dial to the indicated setting giving the desired cooking temperature and setsthe timer 40 for the predetermined cooking period. Setting the timer 40 causes the cam surface on its dial housing 44to contactthetimeroperated cam 49 so causing rotation of the trigger 47. Rotation of the trigger 47 removes the slider actuating cam 50 from the bottom edge of the slider 33. However the slider remains in its raised position since the cam ear 39 in the opening 38 of the slider 33 is supported by the surface of cam 45 on timer spindle 41.Since the slider 33 is still in the raised condition, knob 37 is still tending to push knob 58 upwards thus maintaining the weights on pressure valve 14 in their lowered position. The mechanism is now in the position illustrated in Figure 4(c).

As the timer 40 slowly rotates during the cooking period the cam 45 on timer spindle 41 also slowly rotates until at the end of the predetermined period the cam ear 39 can enter a notch in the cam surface 45, as shown in Figure 4(d), so that the slider descends to its lowermost position In this position the horizontal limb 35 of the slider 33 allows the contact 32 of the microswitch 28 to open so switching off the power to the heating element. At the same time the knob 37 on the upper limb 36 is lowered so allowing knob 58 on lever 54 to fall, hence raising the other end (end 56) of lever 54.

Raising end 56 lifts the weight on the pressure relief valve 14 allowing the chamber to depressurise. The mechanism is now in the position indicated in Figure 4(d) and is ready for another cycle.

At the end ofthe cooking period the timer preferably actuates an audible and/or visual signal (e.g. a bell and/or light).

If it is desired to allow the chamber to depressurise slowly at the end of the cooking period the turn button 57 can be turned to its horizontal position so removing contact between knobs 37 and 58. The lever 54 is then maintained in such a position that the end 56 is in its lowered position and hence the weights on the pressure relief valve 14 are also in the lowered position.

Figures 5 to 8 illustrate an alternative embodiment to the time/temperature pressure release assembly 19. This alternative construction comprises an outer casing 96 within the lower part of which is mounted an energy regulator 61, the output of which can be controlled by adjustmentof the rotatable control knob 62 mounted on a spindle 63 of the energy regulator 61. Within the hollow interior of the knob 62 is a bar 64 which rotates as the knob is rotated.

Above the energy regulator 61 are chassis members 65, 66 for supporting other elements. An on/off microswitch 67 is supported on chassis member 66.

The microswitch 67 has contacts 68 adapted to be closed by upward movement of a side arm 69 of a slider plate 70. The microswitch 67 controls the power to the heater of the pressure cooker in a similar manner to the microswitch 28 of the first embodiment An indication of the power to the heater is shown by neon indicator lights 71 and 72 mounted on the outside of the casing 60.

The slider plate 70 is adapted to slide between guideways 73 (Figure 7) in the chassis member 65 (the slider plate is not shown in Figure 7). Mounted on top of the slider plate 70 is a knob 74 which acts in a similar manner to the knob 37 of the first embodimentto control operation of the depressurisation linkage assembly.

A clockwork timer 75 is mounted on the chassis member 65. The timer can be manually operated by means of the timer knob 76 and the time setting is indicated by a time scale 77 on the outer casing 60.

The timer 75 is adapted to drive a spindle 78 which passes through a hole 97 in the chassis member 65.

Mounted on the spindle 78 is a cam 79 located in an opening 80 in the slider plate 70. The cam surface of the cam 79 bears again a cam ear 81 of the opening 80. The cam 79 has gear teeth 82 on part of its outer rim 83.

Beneath the slider plate 70 is an extension 84 of the chassis member 65. Freely mounted on the extension is a finger member 85, the arm of which can be contacted by the bar 64 upon rotation of the knob 62. The finger member 85 has a cam surface which bears againstthe cam surface of a cam 86 which is also mounted for rotatable movement on the extension 84. One surface of the cam 86 bears against the bottom edge 87 of the slider plate 70 such that on rotation of the cam 86 by the finger member 85 the slider plate is raised vertically. The cam 86 also has gear teeth 88 which in an operative position are driven by the gear teeth 82 ofthecam 79.

The cam 86 has a resilient extension arm 89 which is-designed to be held under a ridge 90 in the chassis member 65 until the cam 86 is forcibly rotated by, for example, contact with the cam surface on the finger member 85. The cam 86 can also be manually rotated, if desired, by means of the handle 91, which passes through an arcuate slot in the chassis member 66 and through an opening in the outer casing 60. A rotatable safety shield 92 covers portions of the arcuate clot.

The operation of the embodiment of Figures 5 to 7 will now be described with particular reference to Figure 8. In Figure 8, Figures (a), (b), (c) and (d) are diagrammatic representations showing movement of the slider plate 70 and its knob 74, the latter actuating the depressurisation linkage assembly, generally indicated by 93 which operates a pressure relief valve of the weight type, generally indicated by 94. In these figures 95 represents the surface of the cam 86 which bears against the bottom edge 87 of the slider plate 70. Figures 8 (b) and (b2) are diagrammatic representations showing the relationship of the control knob 62, the finger member 85, the cam 86 (only part illustrated) and the cam 79 during the stage represented by Figure 8(b). Similarly, Figure 8 (c1) corresponds to Figure 8(c) and Figure 8 (d1) to Figure 8 (d).In the operation of the cooker, the food is placed in the cooker and the lid is replaced. The time-pressure release assembly is placed in position so connecting the heater to the energy regulator. The position is now as indicated in Figure 8(a), with the slider plate 70 on its lowermost position and hence the contacts 68 of the microswitch 67 are open and the valve 94 is also in the open position. The pressure cooker is then brought up to cooking pressure by turning the knob 62 to a high temperature setting. This causes bar 64 to contact the finger 85, as shown in Figure 8(b1), so that the cam 86 is rotated and the surface 95 raises the slider plate 70 as shown in Figure 8(b). After the bar 64 passes finger 85, the finger can pivot freely, (as shown in Figure 8(b2) so that the knob 62 can subsequently be set to any desired temperature setting.The raising of the slider plate 70 causes closure of the pressure relief valve 94 via pivotal movement of the linkage 93 and closure of the microswitch contacts 68.

When the required pressure is reacted the cooking temperature is set by turning the knob 62 to the required setting (indicated, for example, by a pressure indicator on the lid of the cooker). The timer is then set for the required cooker period. Setting the timer causes the teeth 82 on the timer cam 79 to engage the teeth 88 on the cam 86 so causing the cam 86 to be driven to the inoperative position (shown in Figure 7); it is locked in this position by the arm 89 being located under the ridge 90. With cam 86 in the inoperative position its face 95 is clear of the bottom ofthe slider plate 70. However, the slider plate is retained in its raised position since the cam ear 81 is supported by the surface of the cam 79 as shown in Figure 8(c).

As the timer operates during the timed period the cam 79 slowly rotates with the cam ear 81 running on the major cam diameter. Towards the end of the timed period, the timer enters a quicker run down phase and the cam ear 81 follows the descending profile on cam 79 to the lowest point as shown in Figure 8(d). In this position, which corresponds to the end of the timer cycle, the slider plate 70 is in its lowermost position and the contacts of the microswitch are open, so that the heater is turned off. Also the knob 74 is in its lowermost position so opening the pressure relief valve 94. As in the first embodiment, the timer can actuate on audible or visual signal at the end of the timer period.

The pressure cooker of the second embodiment may be provided with a safety thermostat. This is adapted to override the energy regulator and terminate the heating if the temperature within the chamber exceeds a predetermined temperature.

The pressure cooker of the second embodiment can encorporate a mechanism, similar to that of the first embodiment, enabling the chamber to depressurise slowly at the end of the cooking period.

To ensure all air is expelled from the pressure cooker it may be provided with an additional air relief valve. Such a valve allows air to escape from the cooker until the internal pressure within the cooker is just above atmospheric pressure. At this pressure the air relief valve is designed to close so that the pressure of the cooker is thereafter control able by the pressure relief valve.

Claims (12)

1. A pressure cooker vessel comprising a cooking chamber, an electrical heater for heating the contents of the chamber, a switch for the heater, a pressure release valve adapted to close the chamber, control means for adjusting the output of the heater, said control means including switch means adapted to actuate an operating member to close the pressure release valve and to switch on the heater switch when the control means are adjusted for a first output, a timer and means associated therewith adapted to actuate the operating member to retain the pressure release valve in the closed position and the heater switch in and on position when the control means are adjusted for a second output lower than the first, said timer and associated means being adapted to actuate the operating means to open and pressure release valve and to switch off the heater switch after a predetermined time period.

2. A pressure cooker as claimed in Claim 1 wherein the control means for adjusting the output of the heater comprises an adjustable thermostat control.

3. A pressure cooker as claimed in Claim 1 wherein the control means for adjusting the output of the heater comprises an adjustable energy regulator.

4. A pressure cooker as claimed in any one of claims 1 to 3 wherein the operating member is adapted to move in a single plane between a first position where it is adapted to actuate the heater switch to the off position and the pressure relief valve to the open position and a second position where it is adapted to actuate the heater switch to the on position and the pressure relief valve to the closed position.

5. A pressure cooker as claimed in Claim 4 in which the operating member is in the form of a plate adapted to slide between the first and second positions.

6. A pressure cooker as claimed in any one of the preceding claims wherein the means associated with the timer carries a cam surface which is adapted to be driven by the timer and which co-operates with a surface on the operating member such that the operating member is adapted to move after the predetermined time period controlled by the timer from a position in which the pressure release valve is in the closed position and the heater switch is in the on pqsition to a position where the heater switch is in the off position and the pressure release valve is open.

7. A pressure cooker as claimed in any one of the preceding claims in which the pressure relief valve comprises a relief valve having a valve member and a valve seating, one of which acts against the other under pressure of biasing means to close a valve port opening into the interior of the cooker and the operating member is adapted to relieve the biasing means to open the valve by means of the actuation of a pivotally mounted linkage.

8. A pressure cooker as claimed in Claim 7 wherein the biasing means on the relief valve are provided by a weight.

9. A pressure cooker as claimed in any one of the preceding claims wherein the switch means comprises a resilient member which on adjustment of the control means for the first output is adapted to actuate a rotatable member having cam surfaces, one of said cam surfaces being capable of actuating the operating member to a position where the pressure release valve is closed and the heater switch is switched on.

10. A pressure cooker as claimed in any one of Claims 1 to 8 wherein the switch means comprises a a finger member having a cam surface which on adjustment of the control means for the first output co-operates with a rotatable member such that the rotatable member is moved from an inoperable position to a position where it actuates the operating member, the rotatable member having gearing such that it may be returned to the inoperable position after the predetermined time period.

11. A pressure cooker substantially as described herein with reference to and as illustrated in any one of Figures 1 to 4 of the accompanying drawings.

12. A pressure cooker substantially as described herein with reference to and as illustrated in any one of Figures 5 to 8 of the accompanying drawings.