DESCRIPTION

The piesent invention lefeis to improvements in the 1 efngeratmg cncuits of household and sirmlai l efπgeration apparatuses (refrigerators, freezeis and the bke) of the type comprising a hermetically sealed compressoi , which is driven by an electric brushless, electronically controlled motoi , and electromagnetic valve means that aie adapted to cut off the flow of the refrigerant medium upstream of the expansion device

A well-known diawback of I efngeratmg circuits of the above mentioned kind is due to the fact that, dunng the pauses determined by the control thermostat of the appliance in the opei ation of the compiessor, part of the leπigerant medium migrates fiom the condenser (le. the warmest portion of the thermo-fluid-dynamic cncuit) to the evaporator (coldest portion) thioug the capillary tube that forms the expansion device foi the refrigerant medium When the compressoi then restarts aftei such a pause, lefngei ant medium in the gaseous state is already piesent at the inlet of said capillaiy tube As a result, the refrigeration effect is extiemely reduced foi a certain time aftei compressor restarting. In other words, the motoi driving the compiessoi uses electric energy for pioducmg a 1 educed amount of lefngeiation

To the puipose of pi eventing the lefngerant medium from migrating in the above cited manner, as well as to avoid wasting during said compressoi pauses the eneigy used to cieate the lequired piessure diffeience between the circuit

section "upstream" of the compieεsoi and ^f he c u section "downstream" of the compressor, the addition of appiopnate valve means to the refrigerating circuit has been proposed already many years ago The constant presence of refrigerant medium in the liquid state at the inlet of the capillary tube is also ensured

Pressostatic, le piessure-sensitive valve means aie for instance known which when added directly to a refrigerating circuit, advantageously cut off the flow of refrigerant medium in the capillary tube during the thermostatically determined pauses of the compiessoi , and which are then capable of automatically restoring said flow each time that the same compiessor is restarted (see document US-A-4 267 702) Howevei , these piessostatic means due to their being of the mechanical type and requiring construction modifications, particularly in the form of welded oi mechanical joints that in all cases constitute as many potential refrigerant leakage souices, consideiably contribute to a reduction m the overall lebabibty of the l eft lgei atmg circuit

Other valve means pioducing similai effects as the above cited ones are also known, which are operationally bnked with temperature sensors (see document US-A-4 286 438) These othei means do not lequire any modification to the lefπgeiating circuits, however, the unavoidable thermal inertia and the practical difficulty in identifying a rebable position m which to locate the sensois, usually on the coils of the condensei of the lefngeiating circuit, le on the outside of the leπigeration appbance, generally pi event the opening and closing of said valve means fiom being coπectly and lebably timed with the start and stop cycbng of the motoi dnvmg the compressoi

A further drawback that iβsults m connection with the refrigerating circuits of household appbances provided with the above cited valve means and a compiessor dπven by an induction motoi which is either not provided with an electric starting capacitoi oi not Oversized", bes m a substantial impossibibty foi the compiessor to lestart with an unbalanced pressure in the circuit due to the piesence of the above cited valve means The pioposal has therefore been made foi a "contiol valve", le a check valve, to be used inside the shell of the

hermetically sealed compressoi ad±tion to said valve means (see document WO 94/18512) The need foi using motors with a high starting torque is m fact avoided but no significant impiovement in the oveiall efficiency of the system is actually obtained in this mannei Furthermoie, such a solution makes it necessary foi new variants to be added to the vanous compressor model ranges, since not all lefngeiating cπcuits actually lequire the use of said valve means For manufacturers this of course means an assured increase in operating and management costs

In oidei to ebminate such drawbacks the present invention has theiefore following puiposes

to lebably and fully pi event the lefngeiant medium fiom migiatmg from the condensei to the evapoiator dunng pauses in the operation of the compressor

- to minimize the cost burden to be sustained by manufacturers (so as to avoid substantial, undesned increases in the end-user prices to be paid for buying the appbances) by doing away with any need foi oversizmg (lamination stacks and/or coppei windings) the motoi s used to drive the compressoi s,

to minimize nsks affecting the oveiab lebabibty of the refπgei ating circuits, and, above ab

- to l educe eneigy consumption

These aims aie leached in a refrigerating circuits having the features and chaiactenstics as lecited in the appended claims

In particulai , it has been found advantageous to use, in the I efngeratmg ciicuit, a heimehcally sealed compressoi driven by an electiomcally controlled brushless motoi of the type described in the Euiopean patent EP-A-0 490 089 filed by the same Appbcant and furthermoie, to make use of the same motoi control electronic system to contiol a valve that is added to the lefngeiating circuit m a position

3 SUBSflTUTE SHEET (RULE 26)

upstieam of the capibary tube Λs a mεttei of fact this kind of compressor driving motoi , furthei to impioving the overall efficiency (COP) of the 1 efngeratmg circuit, cutting energy usage and reducing noise levels, is capable of restarting without any pioblem, as well as without any need foi using an electric starting capacitoi , even in the presence of such unbalanced piessures as the ones due to the presence of valve means

The invention will anyway be moie leadily and clearly understood from the description of a preferred embodiment that is given below by way of non-brmting example with I efei ence to the accompanying drawings, in which

Figure 1 is a block diagiam of a I efngeratmg cncuit accoiding to the present invention,

- Figui e 2 is diagi ammatical view of the evolution patterns of the pressui es of the lefngeiant medium at the suction and debvery sides of the compiessor du ng a certain time of opeiation thereof

As lllustiated in Figuie 1 , a refngeiating circuit foi a household or sirmla lefiigeiation appaiatus compnses a hermetically sealed compressor 1 , whose shell also encloses the d vmg motoi , a condensei 2, a dehydrator-filtei 3, a capillaiy tube 4 foi the substantially lsoenthalpic expansion of the refngerant medium, and an evapoi atoi 5

As this has alieady been indicated eaibei in this description, the compressoi 1 is of the type descnbed in the afoie mentioned patent EP-A-0 490 089 to the same Appbcant, le of the type dnven by a biushless motoi associated to a frequency contiol anangement 7 Said fiequency contiol arrangement is such as to ensuie that, undei any load condition whatsoevei , the motoi is capable of operating at an automatically conti oiled lotational speed that optimizes the perfoimance of the compiessoi , said lotational speed being in all cases slowei than the lated one, detei mined by the fiequency of the powei supply system, of an equivalent induction motor of the ti aditional type The connection between the compressoi 1

and said frequency control arrangement 7 is established any appropriate manner, in particular through conventional electric wires 6.

In the section of the refrigerating circuit comprised between the condenser 2 and the capillary tube 4, preferably between the outlet section of the condenser 2 and the mlet section of the dehydrator-filter 3, there is arranged a bistable, unidirectional valve 8 of any per se known type, eg. the one described in the document IT-A-1 203 572. .Any other type of valve may however be used, provided that it is of the type that absorbs power only in the switching transients from the closed position to the open one, and vice-versa, in order to avoid using energy unnecessarily.

According to a mam feature of the present invention, the operation of the bistable valve 8 is interlinked with the same frequency control arrangement 7 which also the operation of the motor driving the compressor 1 is actually interlinked with. Even in the case of the connection between the valve 8 and said frequency control arrangement 7, this can be estabbshed in any appropriate manner, in particular through conventional electric wires 9.

And it is exactly the use of a single arrangement 7 for controlling a single functional parameter, le. the frequency, that ensures, according to the present invention, the operation of the valve 8 according to the desired logics, le. ensuring a correct timing between the opening and closing instants of the valve 8 and the start and stop cycles of the driving motor of the compressor 1.

JAS a confirmation of the therewith obtained results, experimentally derived diagrams of the pressure immediately "downstream" (DOWN) and "upstream" (UP) of the compressor 1 at any time in the bfe cycle of a household refrigeration appaiatus provided of a refrigerating circuit according to the present invention aie shown in Figure 2. For reasons of greater simpbcity, the time considered in this instance comprises only two periods of operation (indicated at 1A and 2A) and an intermediate period of pause (indicated at IB) of the compressor. Starting from the instant at which the compressor is started (point zero in the diagrams of Figure 2),

the "downstieam" pressuie uses fiom εn initial lowei value p' _e to an upper value p" _β and stabώzes at such uppei value thioughout most of the period of operation 1A which teiminates at the instant Tl , when the compressor is switched off and stops operating (due to the contiol thermostat of the apparatus tripping in the well-known mannei) During that same period 1A, the "upstieam" pressuie deci eases rapidly from an uppei initial value p', to a sbghtly lower value p", and then remains substantially unaltered until the final instant Tl Starting from said instant Tl , and throughout the entne period of pause IB of the compiessoi (terminating with the same compressoi lestarting at the instant T2), the "downstream" pressuie decreases fiom the initial value p' _β to a final value p'" _e , while the "upstream" piessme uses fiom the initial value p", to the final value p'", In the subsequent period of opei ation 2A of the compi essoi , which starts at the instant T2 and teiminates at the instant T3, the "downstream' pressuie uses again fiom the lowei value p'" _e to the uppei value p" _e , while the "upstream" pressure deci eases again fiom the uppei value p'", down to substantially the lowei value P ^" .

This clearly demonstiates that, during the period of pause IB of the compiessoi no significant migi ation of lenigerant medium actually takes place fiom the condensei 2 to the evapoiatoi 5 In fact, at the instants zero and T2, simultaneously with the compiessoi 1 starting (oi le-startmg), the control airangement 7 commands the bistable valve 8 to switch over to the opening configui ation, wheieas at the instants Tl and T3 the same control airangement commands the same valve to switch ovei to the closing configui ation Theiefoie a lemaikable piessuie diffeience (p'" _e - p'"ι) between the "upstieam" section and the "downstieam" section of the compiessoi 1 keeps persisting even at the end of the pe od of pause, as this can be best seen also in Figuie 2 A major advantage of the biushless motoi inteibnked with a fiequency control anangement of the type used also m the piesent invention lies in the fact that it starts most coirectly and easily also in the presence of these conditions of unbalanced piessure, without any need a sing foi the additional use of a stalling capacitoi as this is on the contrary the case with the tiaditional induction motoi s

_J A _S it has alieady been pointed cut earlier in this description, the present invention is also effective in enabbng significant energy saving effects to be obtained in the operation of the apparatuses equipped with the above described refrigerating circuit, ie. in enabbng said apparatuses to considerably cut then energy usage. As a confirmation thereof, a table appears below which sets forth the results of comparative tests earned out by the Appbcant on the same residential-type upright freezer provided with a refrigerating circuit comprising:

(a) a compressor driven by an induction motor of a traditional type having a power rating of 72 Watt and provided with a starting capacitor with a rated capacitance of 45 microfarad;

(b) a compressor driven by a brushless-type motor having substantially the same power rating as the one cited above, mterbnked with a frequency control airangement in the conditions as described in the repeatedly above cited European patent EP-A-0 490 089 to the same Appbcant; (c) in addition to the compressor as under (b) above, a bistable unidirectional valve arranged in the circuit as shown in Figure 1 and interbnked, according to the teachings of the present invention, with the same frequency control arrangement of the compressoi diivmg motor, lespectively.

The deep-freezer used m the above cited test runs had a net useful volume of 230 btres and a I efngeratmg circuit fiUed with the same charge (80 g) of lefngeiating medium R600 for holding an even, equal temperature inside the apparatus.

Test results

The advantage offered by the piesent mvenhon can be clearly and fully appreciated [case (c)], even when compared with the lnheiently remarkable lesults that can already be obtained with the solution disclosed in the previous patent appbcation filed by the same Appbcant [case (b)] Considering that, m ordei to obtain a correct timing of the opening and closing cycles of the valve with the start and stop cycles of the compressor motoi use is made of one and the same frequency control arrangement, the above advantages are obtained without the manufactuiei having to sustain any substantial increase in costs and, therefore, the selling price of the household refrigeration apparatus equipped with the lefngei ating circuit according to the present invention being affected to any significant extent

hough the piesent invention has been descnbed on the example of a piefeired embodiment theieof, those skilled in the art are fully capable of developing furthei vanants and embodiments from the teachings of the present invention, eg by having lesort to a different functional electric parameter to contiol through one and the same airangement both the compressoi driving motor and the electromagnetic valve means, being it possible for the latter to be formed by means diffeient fiom the above cited bistable unidirectional valves as this has already been said eaibei in this description It wiU therefore be appieciated that any such othei vaiiant of embodiment shall be considered as not departing fiom the scope of the piesent invention