GB2413624A - Multi-function evacuating system in cooling apparatus - Google Patents

Abstract

Cooling apparatus, for example a refrigerator (10), comprises a housing (11) having a casing (11) lined in part of the storage area of the apparatus by thermal insulation walls (12) defining an evacuatable cavity (12a). The housing (11) also contains an evacuatable storage compartment (13). For evacuating the cavity (12a) and the compartment (30) the apparatus comprises evacuating means in the form of a multi-stage pump unit (16) in which the stages (17, 18) thereof are operable in series to maintain the underpressure in the cavity and in parallel to produce underpressure in the compartment. Valves (22, 23, 24) are provided to switch the stages between serial and parallel operation and to selectively connect the stages exclusively with the wall cavity and exclusively with the compartment.

Description

2413624

MULTI-FUNCTION EVACUATING SYSTEM IN COOLING APPARATUS

The invention relates to cooling apparatus and has particular reference to a multi-function evacuating system In such apparatus.

Cooling apparatus, including refrigerators, freezers and refrigerator/freezer combinations, normally have housings with thermal insulation walls insulating the housing interior from the higher temperature level prevailing in the ambient atmosphere. Such walls, whether with or without a partial insulating material filling of, for example, porous foam, can be evacuated so that insulation is provided by a vacuum barrier between the apparatus Interior and exterior. However, unless the wall is skinned with gas-impermeable material, such as stainless steel, and all joints are fully hermetically sealed, it is necessary to maintain the evacuated state of the wall cavity by constant air extraction to compensate for permeation through the wall. For this purpose there is used, for example, an evacuating pump which is required to have a relatively high vacuum capability, such as 10 millibars absolute pressure, but, in view of the requirement to merely maintain an established environment, a low flow rate.

Proposals have also been made to equip apparatus of this kind with an evacuatable storage compartment for storage of articles, particularly foodstuffs susceptible to perishing when In contact with oxygen, In a vacuum environment. The vacuum has to be re- established on every occasion the compartment is accessed to insert or remove articles.

For this purpose there is needed a vacuum pump having a much lower vacuum capability, such as 200 millibars absolute pressure, but a high flow rate to minimise the time to evacuate the compartment. Consequently, in the case of apparatus equipped with both evacuatable thermal insulation walls and an evacuatable storage compartment the conflicting demands imposed on the evacuating system as a whole could be met only by use of two pumps of different capability separately satisfying the different vacuum level and flow rate requirements of the wall cavity and the compartment. This duplication of pumps not only increases costs, but also increases overall susceptibility to failure as well as to generation of noise and vibration and may reduce the storage space or space available for accommodating other components of the apparatus.

The principal object of the Invention is therefore to provide cooling apparatus in which the conflicting requirements of evacuating a thermal insulation wall cavity and a vacuum storage compartment can be resolved by an evacuating system without the cost and l space penalties characterizing existing systems. A further object is the provision of a simplified system inherently less susceptible to failure and having the potential of functioning with reduced development of noise and vibration.

Other objects and advantages of the invention will be apparent from the following

description.

According to the present invention there is provided cooling apparatus comprising a housing having an evacuatable thermal insulation wall cavity and containing an evacuatable storage compartment, and evacuating means for maintaining underpressure in the wall cavity and producing underpressure in the compartment, the evacuating means comprising a plurality of evacuating stages operable in series for evacuating the wall cavity and in parallel for evacuating the compartment.

In this apparatus the different requirements for maintaining the evacuated state of the thermal insulation wall cavity and for rapidly reestablishing the vacuum environment of the storage compartment, in particular the need for a high vacuum capability and low flow rate for the former and a low vacuum capability and high flow rate for the latter, are met by use of a multi-stage evacuating system with alternative serial operation and parallel operation of the evacuating stages. Serial operation results in a high-vacuum, low-flow characteristic appropriate to maintenance of a given level of underpressure in the wall cavity, thus continual compensation for inevitable leakage, whereas parallel operation results in a low- vacuum, high-flow characteristic appropriate to rapid evacuation of the storage compartment. These different characteristics are realised in simple manner by different functional linking of two or more evacuating stages able to act on both the wall cavity and the compartment, rather than by entirely separate systems each individually co-operating with a respective one of the cavity and the compartment.

The evacuating means preferably comprises a multi-stage pump unit which can be, for example, a compact unit with two or, if desired for a specific application, more stages. A particularly compact construction can be achieved if the unit is a twin-chamber pump with oppositely acting displacement elements, such as diaphragms, preferably with a common drive derived from a point intermediate the chambers. The reciprocated masses and the generated pump pulses can be synchronized in such a way as to place both the mechanical forces and fluid flow forces substantially in balance and thus reduce vibration.

Other forms of pump are equally possible, however, including twin-rotor rotary pumps, twin-chamber, single-rotor rotary pumps, gear pumps, twncylinder piston pumps, etc. The displacement elements can be actuated by a mechanical drive, such as a crank, an eccentric or a cam, or, if appropriate, by an electrical, electromechanical, magnetic, hydraulic or pneumatic drive.

The apparatus preferably comprises switching means operable to connect the evacuating stages either exclusively with the wall cavity or exclusively with the storage compartment.

The switching means thus controls the evacuating means to act Just on the wall cavity or just on the compartment and can be further operable to switch, preferably simultaneously, the stages between serial operation and parallel operation in dependence on the connection thereof with the cavity or compartment. The switching means thus controls a dual-mode operating capability of the evacuating system to, in practice, produce underpressure in the compartment when a change in storage conditions therein takes place or restore the level of underpressure in the wall cavity when this is compromised by ingress of air.

The switching means can be automatically operable and, additionally or alternatively, manually operable. Automatic operation is appropriate to apparatus intended to be self- administering and in a preferred embodiment of the invention the apparatus includes detecting means to detect the pressure level in at least one of the wall cavity and the compartment and to automatically operate the switching means in dependence on the detected level or levels. In relation to maintenance of the wall cavity underpressure, the detecting means can trigger the switching means to initiate evacuation of the cavity as soon as the pressure level therein falls below a threshold value. Similarly, the switching means can be triggered to initiate evacuation of the storage compartment if the associated pressure level exceeds a respective threshold value. In that case, however, operation of the switching means should be inhibited if the compartment is unsealed, thus if a compartment door is open. Control of operation of the switching means is therefore preferably subordinate to detection of the door closure state.

The switching means itself preferably comprises a plurality of routing valves, particularly two-way valves, incorporated in ducts interconnecting the wall cavity, compartment and evacuating stages. Various forms of duct interconnection and valve disposition are possible. The valves are, for preference, electrically actuable, such as by way of an electronic control circuit of the apparatus.

Operation of the evacuating stages in parallel can also be employed to maintain an established state of underpressure in the storage compartment if, notwithstanding sealing of the compartment, leakage should occur. In a modification, however, the evacuating stages are additionally capable of operation in series for this purpose.

The cavity is preferably present in a plurality of thermal insulation walls bounding part of the interior space of the housing. Typically, the housing has an external metal casing with an open side closable by a door and, internally of the casing, double-skinned thermal insulation walls lining the casing. The walls could, in fact, contain more than one evacuatable cavity. Such apparatus can be, for example, a refrigerator, freezer or refogerator/freezer combination, particularly - but not necessarily - a domestic appliance.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a schematic view of cooling apparatus embodying the invention, showing the apparatus in outline form and an associated evacuating system as a circuit diagram; Fig. 2 is a diagram of the evacuating system in one operating mode; and Fig. 3 is a diagram similar to Fig. 2, but with the system in another operating mode.

Referring now to the drawings there is shown in Fig. 1 cooling apparatus 10, in this instance a domestic refrigerator, comprising a housing with a metal casing 11 lined, in the storage area of the apparatus, by doubleskinned thermal insulation walls 12 with an evacuatable cavity 12a between the wall skins. The skins can be of moulded plastics material The walls partially enclose a storage space which is closed by a door at a front side of the refrigerator and which includes, apart from conventional shelves and other storage or deposit fittings, a vacuum storage compartment 13 for storage of foodstuffs in a vacuum environment. The compartment 13 basically consists of a box of desired shape and dimensions closable by a respective door.

A pedestal of the refrigerator housing includes a space accommodating functional components of the refrigerator, such as a compressor unit 14 and a two-stage evacuating pump unit 16 for evacuating both the wall cavity 12a and the compartment 13. The pump unit 16 is indicated by dashed lines in the region of the pedestal and also in diagrammatic form to enlarged scale externally of the housing. The duct system linking the pump unit 16 with the wall cavity 12a and compartment 13 is illustrated in purely schematic form to assist understanding of the circuit arrangement; the duct system can be in any appropriate form depending on the proximity of the pump unit to the cavity and the compartment.

Evaporator and condenser units and pipework associated therewith and with the compressor, which form conventional elements of a refrigerator, are not relevant to the invention and accordingly are not depicted.

The two-stage pump unit 16 is incorporated in an evacuating system so as to be capable of dual-mode operation for evacuation of the wall cavity 12a on the one hand, more particularly maintenance of a predetermined level of underpressure therein, and evacuation of the storage compartment 13 on the other hand, more particularly for substituting a subatmospheric for an atomospheric pressure level in the compartment. In the operating mode for evacuating the cavity, the pump unit has a relatively low flow rate and high vacuum capability and in the mode for evacuating the compartment has a relatively high flow rate and low vacuum capability. The two modes are realised, as explained further below, by varying the functional interrelationship of the evacuating stages in conjunction with switching between connection with the cavity and connection with the compartment.

The pump unit 16, in a construction which represents merely one of various possibilities, comprises two pump chambers 17 and 18 containing displacement elements in the form of diaphragm elements 1 7a and 1 8a, respectively. The chambers 17 and 18 are conveniently defined by opposed cylinders with diaphragms secured at their peripheries to the cylinder walls. The diaphragms 17a and 18a are coupled at centre plates thereof by, respectively, articulated connecting rods 1 7b and 1 8b to a common crank drive 19 intermediate the chambers. The crank drive can be rotated by a simple single-speed electric motor (not shown). As apparent from Fig. 1, the configuration of the crank drive, connecting rods and diaphragms is such that the two evacuating or pump stages operate synchronously and in like phase, but in the opposite sense. The mechanical forces and pumping pulsation forces of the two stages are consequently in balance so as to promote smooth operation with minimum vibration.

As in the case of the pump unit construction, the connection of the chambers 17 and 18 with each other and with the wall cavity 12a and compartment 13 is depicted merely by way of example. The connections can in practice be realised not only by pipes and hoses, but also by, for example, bores or passages machined, drilled or otherwise formed in a body of the unit and by shaped portions of wall and panel elements The ducts are so arranged as to enable connection of the chambers 17 and 18 at inlets 20 thereof with the wall cavity 12a and the compartment 13 and to additionally enable connection of the chamber 18 at an outlet 21 thereof with the inlet 20 of the chamber 17. The outlet 21 of the chamber 18 is alternatively connectible with the free atmosphere. The chamber 17 is permanently connected at an outlet 21 thereof with the free atmosphere. Control of the connections is by way of three electrically actuable twoway routing valves 22, 23 and 24, which are located close to the chambers 17 and 18 to minimise loss in efficiency due to compressibility and actuation of which is controlled by an electronic control circuit (not shown) of the refrigerator 10. Depending on the respective setting of the valves, the chambers 17 and 18 are either connected in series with just the wall cavity 12a or in parallel with just the compartment 13. The valve 22 lies in a branched duct linking the inlets 20 of the two chambers 17 and 18 with the cavity 12a and the compartment 13, the valve 23 lies in a duct linking the outlet 21 of the chamber 17 alternatively with the free atmosphere and with the inlet 20 of the chamber 17, and the valve 24 lies at a junction of the inlet 20 of the chamber 17 with the duct from the outlet 21 of the chamber 18 and with the branched duct leading to the cavity 12a and compartment 13.

When the level of underpressure in the wall cavity 12a is to be restored, the two chambers 17 and 18 are connected in series exclusively with the cavity as shown in Fig. 2. In that case, the valve 22 is actuated to connect the cavity solely with the inlet 20 of the chamber 18 and the valves 23 and 24 are actuated to connect the outlet 21 of that chamber with the inlet 20 of the chamber 17. The valve 23 similarly shuts off the alternative connection of the outlet 21 of the chamber 18 with the free atmosphere and the valve 24 simultaneously shuts off the alternative connection of the inlet 20 of the chamber 17 with the branched duct to the cavity 12a and compartment 13. The evacuating flow path resulting from the described valve settings is represented by arrows in Fig. 2. The pressure drop that can be achieved is at a maximum because a cumulative drop in pressure is achieved via both chambers.

Actuation of the valves 22 to 24 by the electronic control circuit to establish serial connection of the chambers 17 and 18 with the wall cavity 12a and simultaneous actuation of the pump unit drive motor can be in response to detection of the pressure level in the cavity by a detector (not shown). If the detector detects a level below a predetermined threshold, the automatic control circuit automatically actuates the valves and the motor to set in train restoration of the required level of underpressure. Continual compensation for leakage is thereby provided, thus avoiding the need for expensive hermetic sealing, which is often difficult to achieve or maintain, of the wall cavity 1 2a.

If the compartment 13 is to be evacuated, either to re-establish the vacuum environment following opening and closing of the compartment door or to establish such an environment for a first time if the compartment has remained out-of-use and kept at atmospheric pressure, the two chambers 17 and 18 are connected in parallel exclusively with the compartment 13 as shown in Fig. 3. In that case the valves 22 and 24 are actuated to interrupt the connection with the cavity 12a and to place the inlets 20 of both chambers 17 and 18 in connection with the compartment 13 and the valve 23 is actuated to connect the outlet 21 of the chamber 18 with the free atmosphere. The valves 22 and 24 simultaneously interrupt the alternative connection of the outlet 21 of the chamber 18 with the inlet 20 of the chamber 17. The resulting evacuating flow path is similarly indicated by arrows in Fig. 3. Here, the pressure drop that can be achieved is lower, as the effective pumping volume is increased for the same motor torque. However, the pump capacity is doubled by the parallel operation of the chambers and the flow rate is thus increased.

The valve actuation for parallel connection of the chambers 17 and 18 and operation of the pump unit drive motor can similarly be in response to detection of the compartment pressure level by a detector, in conjunction with detection of the closed state of the compartment door Evacuation of the compartment can thus be carried out fully automatically, possibly in association with a manual override to allow user selection of atmospheric pressure in the compartment.

The parallel connection of the chambers 17 and 18 with the compartment 13 could, of course, also be employed for the purpose of restoring the level of underpressure in the compartment if this level should diminish due to leakage notwithstanding a closed and sealed state of the evacuated compartment. It would also be possible, by simple modification of the valve control, to provide serial connection of the two chambers to the compartment; in that case, the valve 22 would adopt the state indicated in Fig. 3 and the valve 24 the state shown in Fig. 2. Control of the valves in this manner could be in response to detection of a change in the underpressure level in the compartment 30 and without detection of a change in the door state The refrigerator described in the foregoing embodiment allows maintenance of an effective vacuum wall insulation and operation of a vacuum storage compartment by way of a single pump unit which satisfies the different requirements of the two vacuum features.

Constructional and operating costs may thus be reduced in relation to prior art systems requiring two separate evacuating pumps.

Claims (13)

1. Cooling apparatus comprising a housing having an evacuatable thermal insulation wall cavity and containing an evacuatable storage compartment, and evacuating means for maintaining underpressure in the wall cavity and producing underpressure in the compartment, the evacuating means comprising a plurality of evacuating stages operable in series for evacuating the wall cavity and in parallel for evacuating the compartment.

2. Apparatus as claimed in claim 1, the evacuating means comprising a multi-stage pump unit.

3. Apparatus as claimed in claim 2, wherein the unit is a twin-chamber pump with oppositely acting displacement elements.

4. Apparatus as claimed In any one of the preceding claims, comprising switching means operable to connect the stages either exclusively with the wall cavity or exclusively with the compartment.

5. Apparatus as claimed in claim 4, the switching means being further operable to switch the stages between serial operation and parallel operation in dependence on the connection thereof with the wall cavity and the compartment.

6. Apparatus as claimed in claim 4 or claim 5, the switching means being automatically operable.

7. Apparatus as claimed in claim 6, comprising detecting means to detect the level of pressure in at least one of the wall cavity and the compartment and to automatically operate the switching means in dependence on the detected level or levels.

8. Apparatus as claimed in any one of claims 4 to 7, the switching means being manually operable.

9. Apparatus as claimed in any one of claims 4 to 8, the switching means comprising controllable routing valves in ducts interconnecting the wall cavity, compartment and evacuating stages.

10. Apparatus as claimed in claim 9, wherein the valves are electrically actuable.

11. Apparatus as claimed in any one of the preceding claims, wherein the evacuating stages are additionally operable in series for evacuation of the compartment.

12 Apparatus as claimed in any one of the preceding claims, wherein the cavity is present in a plurality of thermal insulation walls bounding part of the interior space of the housing.

13. Apparatus as claimed in any one of the preceding claims, wherein the apparatus is a refrigerator, freezer or a refrigerator/freezer.