The present invention relates to a refrigeration plant with compressor, condenser, throttling device and evaporator for a circulating refrigerant, in which the output of the plant is regulated when starting and stopping the compressor. Refrigeration plant of this type exist for example in cooling and freezing refrigerators for domestic use. Fur- thermore, the invention relates to a diaphragm valve for use in such a plant.

In domestic refrigerators a capillary tube is normally used as throttling device. However, this can provide optimum operating conditions only in a narrow range of operating conditions, but it is cheap in production and installation, and reliable in operation. Furthermore, it is easy to bring into thermal contact with the suction pipe between evaporator and compressor. It protects the compressor against fluid shock and prevents the formation of steam on the suction pipe.

The capillary tube allows pressure equalising between condenser and evaporator m the standstill periods of the compressor. This pressure equalising facilitates starting of the compressor after the standstill period, but the condenser is emptied of condensed refrigerant, after which additional hot gas may pass from the condenser to the evaporator. This leads to a certain waste of energy.

At the end of the operation period of the compressor, the distribution of refrigerant in the plant will normally have reached a dynamic equilibrium, which provides optimum operating conditions. This equilibrium is disturbed by the pressure equalisation in the standstill period, so that in the first part of the next operation period of the

compressor, the operating conditions of the plant lie outside the optimum range. This leads to a further waste of energy.

In large refrigeration plant these drawbacks are avoided among other things by using an expansion valve with vari¬ able throttling effect as throttling device instead of a capillary tube, but this solution is too expensive for domestic use, and suitable valves generally need to much installation space.

The passage from the condenser to the evaporator may be closed with an electrically actuated valve in the stand¬ still period of the compressor. However, if a monostable valve is chosen (open or closed when not energised) , the actuation consumes some energy either in the standstill period of the compressor or in the operation period, and this counteracts the desired reduction of energy consump¬ tion. If a bistable valve is chosen, actuation by a current pulse requires a special control device and various other constructional changes of the furniture, which may make the solution too expensive.

From US 4267702 a refrigeration plant of a type described in the preamble of claim 1 is known. Here a flow control valve is inserted between the condenser and the evaporator. The flow control valve reacts to fluctuations of the condenser pressure by cutting off refrigerant flow from the condenser to the evaporator while the compressor is stopped, and releasing refrigerant flow from the condenser to the evaporator when the compressor has been started. This is achieved by carrying out the valve function with a diaphragm whose "opening" side is subjected direct to changes of the condenser pressure, while its "closing" side

receives the changes with a certain delay via a flow restriction.

It seems doubtful, however, whether the very simple valve shown schematically in fig. 1 of the document can be designed to function reliably in practice. In this respect the flow restriction will be critical, because experience shows that openings of less than 0.8 mm diameter will often be choked in practice by inevitable impurities m the refrigeration plant. Furthermore there will be a difference in the effect of the restriction, depending on whether the refrigerant to pass it is gaseous or liquid. Finally, it is doubtful whether sufficient diaphragm movement can be produced when after prolonged operation of the compressor both valve chambers are filled with condensed, perhaps even supercooled refrigerant. In this case the closing movement of the diaphragm must be effected by expansion of the liquid in the chamber 36 when it is decompressed via the diaphragm 34. This means that the diaphragm must have a very short travel between its closed position and its open position, or that there must be a relatively large volume of liquid available in the valve. Both solutions are problematic, a short travel with a view to design and production, and a large chamber volume with a view to the filling and operation of the refrigeration plant.

The practical embodiment of a purely pressure actuated valve shown in the other figures is quite complicated, requiring among other things a two-part condenser m order to function. Perhaps the reason for this complicated design is that it has been difficult to make the simple design work in practice.

It is the object of the present invention, with a simple and reliable valve design to build a refrigeration plant of

the type described above, where the condenser is cut off during the standstill periods of the compressor.

According to the present invention as described in claim 1, the flow control valve comprises a temperature sensor in thermal contact with the suction pipe. The temperature sensor converts a sensed temperature to a sensor pressure, and the flow control valve is a self-acting valve designed for cutting off and releasing flow, respectively, by utilising a difference between the sensor pressure and the pressure in the condenser.

According to this invention, a self-acting function is created by utilising the thermal conditions during operation of the refrigeration plant. The use of a temperature sensor instead of a flow restriction to provide a differential pressure gives greater design freedom, so that it becomes easier to make the required diaphragm travel available, and the valve can be produced with a very small dead volume. As shown by the following description, the valve may otherwise be quite as simply designed as the simple valve described in US 4,267,702. The placing of the temperature sensor in thermal contact with the suction pipe gives rather large temperature deflections. This means that rather large pressure fluctuations are available for the function of the valve, which gives a reliable and safe function.

The patent claims 2 to 6 give further details about the construction of the invention.

In refrigeration plant in which throttling is made with a capillary tube, part of this tube can be inserted before the flow control valve, as stated in claims 7 and 8. When

suitably dimensioned, this will speed up the closing of the valve at compressor stop.

It is a further object of the present invention to describe a diaphragm valve for the control of the refrigerant flow from a condenser to an evaporator in a refrigeration plant where the diaphragm functions as a valve plate, and which is simple and cheap to manufacture. This is achieved as described in claim 9 in that the valve includes a valve seat element which is mounted off an opening in the valve housing, that the valve seat element has a first lip of elastic material, which surrounds a through-hole in the body and is in sealing contact with the valve housing around the opening, and that the valve seat element has a second lip of elastic material, which surrounds the through-hole and serves as valve seat for the diaphragm.

This design of the valve with two resilient sealing lips has the advantage that it is possible to compensate for production tolerances in the position of the diaphragm by compressing the first sealing lip (between the valve seat element and the valve housing) more or less strongly when the valve seat element is mounted in the valve. This is equivalent to adjusting the position of the valve seat in relation to the diaphragm. Of course the first sealing lip must be dimensioned to be suitably deformable so that the available adjustment range suits the tolerances of the production process.

A movable installation of the valve seat element as described in claims 10 and 11 is advantageous at series production, because the setting can then be effected by means of a calibration piston. The piston is pushed against the valve seat element until the desired position is

reached, for example in relation to a reference surface on the valve housing.

Building up the valve seat element as a resilient element with a surrounding support ring, cf. claim 11, makes the valve seat element easy to handle and to mount precisely.

The present invention is explained in the following with reference to the accompanying drawings, which show concrete examples of embodiments.

Fig. 1 shows a refrigeration plant with a flow control valve inserted between condenser and evapor¬ ator.

Fig. 2 shows a flow control valve for use in the refrigeration plant according to fig. 1.

Fig. 3 shows the cyclical operation of a refrigeration plant without a flow control valve.

Fig. 4 shows the cyclical operation of a refrigeration plant with a flow control valve according to the invention.

Fig. 5 shows, enlarged, the valve seat element of the flow control valve.

Fig. 6 shows the design of the retainer piece of the valve seat element.

Fig. 7 shows the bottom part of the valve with a ref¬ erence surface for the position of the valve seat element.

The refrigeration plant according to fig. 1 is filled with a suitable refrigerant and is driven by a sealed compressor 1 with a suction or input pipe 2 and a pressure or output pipe 3. Compressed refrigerant is fed via the pressure pipe 3 to the condenser 5, which in the concrete example is a meander-shaped tube. The tube 5 is placed so that it may give off heat to the surroundings 31, normally the ambient air.

On its way through the condenser 5 the refrigerant gives off the compression heat, whereby it is condensed to liquid in the lower part of the condenser. The liquid passes a dryer filter 6, and then via a flow control valve 7 and a capillary tube 8 it is led to an evaporator 9. The evaporator is placed in thermal contact with a refrigerated compartment 30, for example in a refrigerator.

At the passage through the capillary tube 8 the pressure of the refrigerant is reduced to a value which is below satu- rated vapour pressure. The refrigerant therefore evaporates in the evaporator 9, thereby absorbing heat from the refri¬ gerated compartment. Via the suction pipe 2 the evaporated refrigerant is led to the compressor 1, where it is recompressed. When a suitably low temperature is reached in the compartment 30, the compressor 1 is stopped by means of a thermostatic switch 32 actuated by a temperature sensor 33 in the compartment 30.

During the standstill of the compressor the temperature in the compartment 30 gradually increases, and when an upper temperature limit has been reached, the temperature sensor 33 actuates the switch 32 again, so that the compressor starts refrigerating the compartment 30 again. Thereby the plant acquires a cyclic operation pattern, and the tempera- ture in the compartment 30 pendles around a desired value.

Fig. 2 shows a cross section, turned 180° in relation to fig. 1, of the flow control valve 7. The valve function is performed by a diaphragm 10, fixed between the upper part 11 and the bottom part 12 of the valve housing. The diaphragm divides the valve housing into two chambers 21 and 24. The valve seat consists of a circular lip 15 on an annular rubber element 13, which is mounted in a retainer piece 14. The part 14 is pressed into a circular recess 16 in the valve bottom 12, so that another circular lip 25 at the bottom of the rubber element 13 seals against the bottom wall 12 of the valve housing around the outlet opening 19. It appears from fig. 1 and fig. 2 that the refrigerant is led through the valve via an inlet connector 17, a duct 18 in the rubber element 13, the duct 19 in the bottom part 12 and an outlet connector 20.

From the chamber or cavity 21 in the top part 11 of the valve, a capillary tube 22 leads to a temperature sensor 23. In the embodiment example, the cavity 21, the capillary tube 22 and the temperature sensor 23 are filled with the same refrigerant as the refrigeration plant otherwise, and the filling has been measured so that there is a liquid/gas interface in the sensor 23, regardless of whether the cavity 21 is gas filled or liquid filled.

Therefore the pressure in the cavity 21, and thereby the pressure on the top side of the diaphragm 10, will always be determined by the temperature of the sensor, whereas the pressure on the bottom side of the diaphragm will generally be equal to the condenser pressure. As long as there is condensed refrigerant in the condenser, the condenser pressure will be determined by the temperature at the liquid/gas borderline in the condenser.

It may be expedient to select a mixed filling for the temperature sensor 23. For instance, the filling could mainly consist of the refrigerant used in the refrigeration plant, but a certain share of a different refrigerant, compatible with the refrigerant in the plant, could be added. Selection of the mixing ratio will to a certain degree have influence on the pressure characteristics of the temperature sensor, and thus on the actuation of the valve.

As shown in Fig. 1, the temperature sensor 23 is placed in thermal contact with the suction pipe 2 and near the compressor 1. As a basis for an examination of the operation of the refrigeration plant the situation is now contemplated where the plant has been out of operation for a long time, so that via the inevitable leaks in the compressor a pressure equalisation has taken place between the various parts of the plant, while at the same time all parts of the plant are at the same temperature.

In this situation the pressure on both sides of the dia¬ phragm 10 will be the same, for which reason it will be in the state of rest shown in fig. 2, where it is lifted from the valve seat. The flow control valve 7 is therefore open for through-flow. When the compressor is started, the condenser pressure, and thus the pressure m chamber 24, rises, and when a sufficient pressure is reached, condensation starts. Therefore, there is a flow, first of gaseous and then condensed refrigerant, through the flow control valve 7 to the evaporator 9 through the capillary tube 8.

When passing through the capillary tube 8, the pressure of the condensed refrigerant is, as mentioned, reduced to a value below saturated vapour pressure. The refrigerant

therefore evaporates in the evaporator 9, thus collecting heat from the refrigerated compartment 30. The cold refrigerant gas from the evaporator is led to the compressor via the suction pipe 2, which is thus cooled. This causes a cooling of the temperature sensor 23, whereby the pressure in the gravity 21 in the flow control valve decreases. The resulting pressure difference between the two surfaces of the diaphragm keeps the valve open during the whole operation period of the compressor.

When compartment 30 has been cooled to the desired temperature, the thermostatic switch 32 stops the compressor 1. Then both the flow of hot compressed gas to the condenser 5 and the flow of cold suction gas through the suction pipe 2 stop, causing the condenser 5 to be cooled and the temperature sensor 23 to be heated.

As the temperature sensor is placed near the compressor, it is not only exposed to heat from the surrounding air, but also to radiated heat from the compressor (which is hot from the operation) , and to pipe heat, namely the heat led back into the suction pipe from the compressor. Thus the heating of the temperature sensor takes place relatively fast, and at the same time the condenser is cooled.

In practice it turns out that, when placed correctly, the temperature sensor 23 gets warmer than the condenser very soon after the stop of the compressor. As the pressure in both temperature sensor and condenser is determined by the temperature, this means that the pressure in the chamber 21 over the diaphragm 10 gets higher than the pressure in chamber 24 under the diaphragm very soon after the stop of the compressor. The diaphragm will therefore deflect to bearing against the valve seat 15, whereby the flow control valve 7 is closed.

Immediately after the closing of the flow control valve, the pressure m its outlet connector 20 decreases heavily. The reason for this is that the outlet connector is connected with the evaporator via the capillary tube 8, said evaporator having a low temperature and thus a low pressure. The outlet connector and the capillary tube are quickly emptied of refrigerant, as the flow from the condenser is cut off, after which the pressure in the outlet connector decreases to evaporator pressure.

The low pressure in the outlet connector 20 ensures that the valve 7 is kept safely closed in the standstill period of the compressor, even if the temperature difference between the temperature sensor 23 and the condenser 5 gets smaller towards the end of the standstill period. The reason for the temperature difference getting smaller is that both the compressor temperature and the condenser temperature approach the temperature of the ambient air. The smaller temperature difference causes that generally the pressure difference between the two surfaces of the diaphragm 10 gets smaller. However, the low pressure in the outlet connector 20 gives the "condenser side" of the diaphragm a deficit of pressure power corresponding to the diaphragm area covering the valve seat, causing that the valve remains closed during the whole standstill period of the compressor.

Thus, there is no loss of condensed refrigerant from the condenser 5 during the standstill period, apart from what might possibly flow backwards through possible leaks in the compressor, and normally there will still be condensed refrigerant in the condenser at the end of the standstill period.

The time from compressor stop to closing of the flow control valve can be reduced by not mounting the flow control valve 7 before the capillary tube 8, but in the capillary tube. In other words, the capillary tube is divided into two parts, and then one (the first) part is mounted between the condenser and the flow control valve, and the second part is mounted between the flow control valve and the evaporator. When using a dryer filter, as shown in the embodiment example, the first part of the capillary tube will normally be mounted between the dryer filter 6 and the flow control valve 7. The reference number 50 in fig. 1 shows this mounting of the first part of the capillary tube. The second part is then mounted in the usual way between the flow control valve 7 and the evaporator 9, cf. reference number 8 in fig. 1.

Throughout the opening time of the valve, the refrigerant flow through the first part 50 of the capillary tube will cause a pressure drop, so that the pressure on the "condenser side" of the diaphragm 10 is lower than the condenser pressure. This causes that at compressor stop the temperature sensor 23 needs less heating to create the pressure across the diaphragm 10, which closes the valve 7, which is not the case when the valve is mounted direct after the condenser. As the required temperature is lower, it will be reached at an earlier stage of the heating course of the temperature sensor, the result is an earlier closing of the valve after compressor stop.

The piece of capillary tube 50, inserted between the condenser 5 and the flow control valve 7, must not necessarily have the same inside diameter as the capillary tube 8 between the valve and the evaporator 9. The capillary tube 50 will normally be considerably much shorter than the capillary tube 8. It will also be possible

to combine the divided capillary tube with a mixed filling of the temperature sensor 23, which gives additional freedom with regard to the adaptation of the system characteristics of the valve to the needs to be met in a concrete refrigeration furniture or the like.

At the next start of the compressor the flow control valve is still closed. The compressor now pumps hot gas to the condenser causing the temperature, and thus the pressure, of the condenser to increase very quickly. Thus, also the pressure ruling on the "condenser side" of the diaphragm 10 is increasing. Practice shows, however, that the increase in the pressure on the "temperature sensor side" of the diaphragm, determined by the temperature sensor 23, is slower, as the housing of the compressor is heated much slower than the condenser. After a short time an overpressure is built up under the diaphragm 10, providing that the flow control valve is opened.

When the valve is opened, the flow of condensed refrigerant to the evaporator 9, and the passage of evaporated cold refrigerant through suction pipe 2, start, whereby the temperature sensor 23 is exposed to a sudden temperature drop. Thus the pressure in the cavity 21 in the flow control valve decreases. The resulting pressure difference between the two surfaces of the diaphragm again keeps the valve open throughout the whole operation period of the compressor, after which the stop and start course described above repeats itself cyclically for as long as the plant is in operation.

The embodiment with a piece of capillary tube between the condenser 5 and the flow control valve 7 has largely seen the same opening characteristics for the valve. This is caused by the fact that there is no considerable flow of

refrigerant through the capillary tube as long as the flow control valve 7 is closed. In this period there will thus be no pressure drop in the part 50 of the capillary tube placed between the condenser 5 and the valve 7. This means that on the "condenser side" of the diaphragm 10 condenser pressure will also be ruling in this embodiment of the plant as long as the valve is closed. The opening time is therefore the same as discussed above.

Contrary to previously known refrigeration plant with capillary tube throttling, the filling and pressure of the condenser in the plant described are maintained by the flow control valve 7 during the standstill period of the compressor. The compressor must therefore be of a type which can start against load. In return, the plant as a whole does not get as far away from the energetically optimum equalisation state during standstill of the compressor as previously known plant of this type.

The pressure conditions in a refrigeration plant tested in practice are shown in fig. 4. The operation and standstill periods of the compressor are shown by the line 35, the condenser pressure measured immediately before the flow control valve is shown by the line 34, and the pressure in the capillary tube measured immediately after the flow control valve is shown with the line 36. The pressure signal in curve 36 thus shows the pressure in the chamber between the flow control valve 7 and the capillary tube 8, i.e. in the outlet connector 20 of the valve. In the periods when no considerable flow of gas or liquid exists through the capillary tube 8, the curve 36 also represents the evaporator pressure.

After the closing of the flow control valve, the pressure in the outlet connector 20, which is connected with the

evaporator 9 via the capillary tube 8, decreases very quickly to the value corresponding to the temperature of the evaporator, whereas the pressure in chamber 24, which is equal to the condenser pressure, decreases stepwise with the cooling of the condenser. This appears from fig. 4, in which the curve 34 shows the slow decrease of the condenser pressure, while the curve 36 shows the sudden pressure drop after the flow control valve 7 occurring when the valve cuts off the flow.

As previously discussed, this sudden pressure drop causes that during the whole standstill period of the compressor the pressure under the part of the diaphragm 10 surrounded by the valve seat 15 is much lower than that on the upper side of the diaphragm.

Further, the diagram shows that after compressor start it takes a few seconds until sufficient pressure has been built up in the condenser to open the flow control valve. This can be seen from curve 36. The suction effect of the compressor reduces the pressure measured right after the flow control valve, until the flow control valve opens and the pressure increases to the pressure level of the condenser.

The diagram in fig. 3 shows the operation of the same refrigeration plant without the flow control valve shown, meaning that the valve has been replaced by a simple pipe connection. Small deviations in the absolute pressure values between fig. 3 and fig. 4 are caused by the fact that the plant has to be drained of refrigerant for the mounting of the flow control valve, after which it is refilled. The filling operation may cause small variations in the amount of refrigerant. Curve 34 in fig. 3 shows that at compressor stop condensed refrigerant is still flowing

to the evaporator, until the condenser is empty. Then hot gas is flowing from the condenser to the evaporator, until the pressure between these two plant parts has been equalised. The condenser pressure will thus drop to a much lower level than in the plant using the flow control valve.

The standstill periods of the compressor are longer in the plant with the flow control valve, and less time is used from compressor start until condensation pressure is reached in the condenser. Both features imply a lower energy consumption.

The attainable energy savings depend on the specific embodiment of the refrigeration plant; in practical tests the use of the flow control valve involved a reduction of the energy consumption by approximately 15%.

Fig. 5 shows a cross-section of the valve seat element 13 and the surrounding retainer piece 14. The lower lip 25 surrounding the central through-bore 18 of the rubber element is higher than, and has at its free end a smaller wall thickness than, the upper lip 15. The lip 25 is therefore soft, and at the same time so high that it provides a safe sealing towards the valve bottom 12, while the valve seat unit 13/14 is pressed more or less down into the bottom part 12, within certain limits determined by the construction.

The retainer piece 14 for the valve seat element 13 is shown from the bottom in fig. 6. The periphery of the retainer piece is shaped with a projection 26, giving a press fit in the circular recess 16 in the valve bottom 12.

Fig. 7 shows the valve bottom 12 with the central recess 16. The bottom part can be manufactured cheaply by means of

solid shaping, for instance deep-drawing, but this gives larger dimension variations than for instance turning. A critical dimension in the valve is the distance between the diaphragm 10 and the valve seat 15. This distance is set by pressing the valve seat element 13 suitably into the valve bottom 12. When comparing fig. 2 and fig. 7 it can be seen that the top surface 27 of the valve bottom can serve as reference surface for this pressing, as the top plane 27 is decisive for the position of the diaphragm. The pressing of the valve seat element 13 can therefore be made with a piston bearing against the top plane 27 and fixing an exactly defined distance from the reference plane 27 to the valve seat 15. Thus only the production tolerances of the diaphragm must be considered when dimensioning the distance between the diaphragm 10 and the valve seat 15, and these tolerances can be kept at a much lower level than those seen when working with deep-drawing of the valve bottom.