Accumulator for a refrigeration system

An accumulator for an automotive refrigeration system is disclosed. The accumulator includes a housing having a cover, an inlet port for introducing refrigerant, an outlet port, and a U-shaped tube having one end connected to the outlet port and an other end opening to the upper portion of the housing of the accumulator at a predetermined level. A conduit is vertically disposed in the housing of the accumulator and has lower end opening into the housing at a level lower than the other end of the U-shaped tube. The upper end of the conduit communicates with the outlet port through a fluid passage. A sight glass is disposed on the fluid passage to view the refrigerant. On charging the system, when refrigerant is in view, the proper volume of refrigerant is enclosed in the refrigeration system.

TECHNICAL FIELD 
This invention relates to an accumulator for a refrigeration system. More 
particularly, this invention relates to an accumulator for an automotive 
refrigeration system which permits detection of the proper volume of 
refrigerant in the system. 
BACKGROUND OF THE INVENTION 
In a refrigeration system including a compressor, a condenser, a fixed 
throttle valve, and an evaporator having an outlet port connected to an 
accumulator, the proper volume of refrigerant in the refrigeration system 
must be maintained. If the proper volume of refrigerant is not enclosed in 
the refrigeration system problems occur. If too much refrigerant is 
enclosed within the system, refrigerant in the liquid phase can be forced 
from the accumulator into the compressor because the capacity of the 
accumulator is too small, and the compressor can suffer damage by 
compressing liquid refrigerant. Also, the compression capacity may 
decrease. On the other hand, if too little refrigerant is in the 
refrigeration system, there may be no refrigerant in the accumulator. The 
temperature of the refrigerant at an inlet port of the compressor 
therefore may increase, and the refrigeration capacity of the evaporator 
will decrease. 
If the accumulator is used in an automotive air conditioner, the volume of 
the accumulator depends on the size of the engine compartment and on 
operational factors which cause the amount of refrigerant in the 
accumulator to vary. Thus, the accumulator should be small enough to fit 
in the engine compartment, but be sized to accommodate refrigerant 
throughout the range of rotational speeds of the compressor, throughout 
the range of thermal loads on the evaporator, and throughout the range of 
thermal loads on the condensor. If properly sized, the accumulator will be 
filled with refrigerant when the rotational speed of the compressor is the 
lowest (i.e, at engine idle), when the thermal load on the evaporator is 
lowest (e.g., when air entering the evaporator has a temperature of 
20.degree. C. to 25.degree. C. and relative humidity of about 50%), and 
when the thermal load on the condenser is highest (e.g., air temperature 
at the condenser inlet is 30.degree. C. to 35.degree. C.). When the 
rotational speed of the compressor and the thermal load on the evaporator 
are the highest (e.g., air temperature at the inlet is 30.degree. C. to 
35.degree. C. and relative humidity is about 50%), there will be virtually 
no refrigerant in the accumulator. 
In a conventional method for measuring the volume of refrigerant, the 
surface temperature of the outlet port of the evaporator is initially 
measured to determine the proper refrigerant amount (if the temperature is 
sufficiently low, the refrigerant volume is proper). However, this method 
has a very low degree of precision. 
Another method for detecting low refrigerant levels involves measuring the 
clutch cycling time (the duration the compressor clutch is on and off). 
The clutch cycling time is shortened when the refrigerant volume is low. 
However, since the clutch cycling time can be shortened by other factors 
as well, it is an imprecise method for detecting the lack of refrigerant. 
One apparatus for detecting the proper amount of refrigerant is disclosed 
in Japanese Utility Model Application Publication No. 57-33343. In this 
application, as illustrated in FIG. 1, accumulator 6 comprises housing 61 
having an open end covered by end plate 62. Inlet port 7 is disposed on 
the upper portion of housing 61 and communicates between the inside of 
housing 61 and an evaporator (not shown). Outlet tube 8 communicates 
between the inside of housing 61 and a compressor (not shown), and a 
conduit 63 vertically extends inside housing 61. End plate 62 has 
depression 64 which is covered by sight glass 65 to form a small space. 
One end of conduit 63 is open to depression 64 which communicates with 
outlet tube 8 through passageway 66. The other end of conduit 63 extends 
to the lower portion of housing 61 to draw gaseous refrigerant and 
entrained lubricating oil to outlet tube 8 though depression 64 and 
passageway 66. Accordingly, if the liquid refrigerant passes through 
depression 64 its existence can be confirmed through sight glass 65. 
However, liquid refrigerant may flow past sight glass 65 even when 
refrigerant volume is improper. Moreover, because conduit 63 and 
passageway 66 return some lubricating oil to housing 61, liquid can be 
detected whether or not refrigerant exists in the lower portion of housing 
61. In addition, when the volume of accumulator 6 is minimized as 
required, it is difficult to properly detect refrigerant therein by this 
method. 
Another known accumulator 6, as shown in FIG. 2, includes inlet port 7 and 
U-shaped tube 9 integrally formed with outlet port 8. U-shaped tube 9 is 
provided with lower opening 91 for returning lubricating oil to the 
accumulator and upper opening 92 for equalizing pressure. Immediately 
after the compressor stops, a pressure difference is produced between the 
compressor and accumulator 6 causing liquid refrigerant to flow into 
U-shaped tube 9 through hole 91 and into the inside of the compressor. 
Since U-shaped tube 9 is provided with hole 92 to equalize the pressure 
difference, the compressor does not does not compress liquid refrigerant 
when the compressor is restarted. However, in the above accumulator, it is 
impossible to detect the refrigerant volume in the refrigeration system. 
SUMMARY OF THE INVENTION 
It is a primary object of this invention to provide an accumulator for an 
automotive refrigeration system which properly detects the volume of 
refrigerant in the system. 
It is another object of this invention to provide an accumulator for an 
automotive refrigeration system which prevents liquid refrigerant from 
flowing out of the accumulator. 
It is still another object of this invention to provide an accumulator for 
an automotive refrigeration system which prevent superheating the liquid 
refrigerant at an outlet port of an evaporator. 
It is still another object of this invention to provide a compact 
accumulator for an automotive refrigeration system. 
An accumulator for an automotive refrigeration system according to the 
present invention includes a housing having a cover, an inlet port for 
introducing a two phase mixture of refrigerant (and lubricating oil) from 
an evaporator, an outlet port for withdrawing gaseous refrigerant from the 
accumulator, and a U-shaped tube. The U-shaped tube is connected at one 
end to the outlet port and is positioned at a predetermined level at its 
other end. A conduit vertically extends within the interior of the 
accumulator having its lower end opening below the other end of the 
U-shaped tube. The upper end of the conduit is connected to the outlet 
port through a fluid passage formed at a level above the other end of the 
U-shaped tube. A sight glass is disposed on the fluid passage to view 
liquid refrigerant. The U-shaped tube may be provided with a hole for 
returning lubricating oil to the accumulator at its lowest portion. 
Various additional advantages and features of novelty which characterize 
the invention are further pointed out in the claims that follow. However, 
for a better understanding of the invention and its advantages, reference 
should be made to the accompanying drawings and descriptive matter which 
illustrate and describe the preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 3, a refrigeration circuit including an accumulator 
according to the present invention is shown. The refrigeration circuit 
generally comprises compressor 1, condenser 2, fixed throttle valve 3, 
evaporator 4, and accumulator 5. These basic components are coupled in 
series to form a conventional refrigeration circuit. The arrows indicate 
the direction of flow of refrigerant. Gaseous refrigerant is compressed in 
compressor 1 and supplied to condenser 2 where it is cooled by rejecting 
heat to the ambient air and condensed to liquid refrigerant. The liquid 
refrigerant is delivered to throttle valve 3 where it expands. The 
refrigerant emerges from throttle valve 3 as a two phase mixture of liquid 
and gas, primarily liquid. As the two phase mixture of refrigerant flows 
through evaporator 4, which acts as a heat exchanger, heat is transferred 
to the refrigerant from incoming air (such as interior air in the vehicle 
passenger compartment), and the refrigerant vaporizes and assumes its 
gaseous state. This gaseous refrigerant flows into accumulator 5. 
Referring to FIG. 4, the construction of accumulator 5 in accordance with 
the present invention is shown. Accumulator 5 comprises cylindrical 
housing 51a having an upper opening covered by cover plate 51b, fluid 
inlet port 7 formed on the outer peripheral surface of housing 51a, fluid 
outlet port 8 formed on cover plate 51b, and U-shaped tube 52 disposed 
within the interior of housing 51a. U-shaped tube 52 is supported within 
housing 51a by connection to the inner end opening of outlet port 8 to 
form a fluid outlet passage. Cover plate 51b is provided with concave 
depression 57 at its upper end surface. Depression 57 is covered by cap 58 
to form small gap 59. Cap 58 has a sight glass 54 to permit viewing small 
gap 59. Small gap 59 communicates with the interior of housing 51a through 
conduit 53, and communicates with outlet port of 8 through U-shaped tube 
52 and connecting way or bore 55 which is formed in cover plate 51b. 
Therefore, conduit 53, small gap 59, and connecting way 55 define a fluid 
passage between the interior of housing 51a and the outlet portion of 
U-shaped tube 52. 
The free end of U-shaped tube 52 is open to the upper portion of housing 
51a at level L1 as shown in FIG. 4. Conduit 53 vertically extends within 
the interior of housing 51a having its lower end at level L2 which is 
slightly lower than level L1. Also, oil return hole 56, formed on the 
lower portion of U-shaped tube 52 at level L3, is placed near the bottom 
portion of housing 51a and is below L2. 
The difference between level L1 and level L2 is set so when the two phase 
mixture of refrigerant is drawn into the interior of housing 51a through 
inlet tube 7 and the refrigerant exceeds level L2, liquid refrigerant is 
drawn into conduit 53 and flows through small gap 59 and connecting way 55 
to outlet port 8 by the pressure difference between the opening of conduit 
53 in housing 51a and outlet port 8. The flow of the two phase refrigerant 
mixture may be visually inspected and its existence confirmed through 
sight glass 54, thereby indicating that the refrigerant level in 
accumulator 6 exceeds level L2. The highest level of refrigerant in 
accumulator 6 should be between L1 and L2. 
Accordingly, if accumulator 5 is properly sized to accommodate the range of 
rotational speeds of compressor 1 and the range of thermal loads of 
evaporator 4 and condenser 2, and the system is charged with the correct 
volume of refrigerant, the level of refrigerant in accumulator 5 should 
very from a low point just above L3 to a high point between L1 and L2. The 
highest level will be achieved with compressor 1 at idle, the thermal load 
on evaporator 4 at a minimum, and the thermal load on condensor 2 at a 
maximum. Conversely, the lowest level of refrigerant in accumulator 5 wil 
be achieved when the rotational speed of compressor 1 and the thermal load 
on evaporator 4 are at their maximums. 
The method of properly enclosing refrigerant (i.e., charging the system) is 
as follows. The refrigeration system is maintained with the rotational 
speed of compressor 1 at its lowest level (i.e, at idling of the engine), 
the thermal load on evaporator 4 at its lowest level, and the thermal load 
on condenser 2 at its highest level. Then the refrigerant is enclosed in 
the refrigeration system. While enclosing the refrigerant, the amount is 
confirmed through sight glass 54. If the flow of refrigerant is visually 
confirmed, enclosing should cease, because, as described above, this 
indicates that the refrigerant level has surpassed level L2. Therefore, 
the proper amount of refrigerant is enclosed within the refrigeration 
system. 
Furthermore, since level L1 of the opening of U-shaped tube 52 is set 
slightly higher than level L2 of the oening of conduit 53, any excess 
liquid refrigerant in accumulator 5 is prevented from flowing out of 
accumulator 5 into compressor 1 by flowing into and residing in U-shaped 
tube 52. This compensates for the situation where the refrigeration system 
operates under conditions causing the thermal load on evaporator 4 to be 
slightly lower than the lowest expected load and the thermal load of 
condenser 2 to be slightly higher than the highest expected load, and the 
actual volume of refrigerant enclosed in the refrigeration system is 
slightly greater than the required volume (occasioned, for example, by 
slight overcharging). Also, the fluid passage which comprises connecting 
way 55, concave depression 57, small gap 59, and conduit 53 functions as a 
pressure equalizer. This prevents liquid refrigerant from being drawn out 
of accumulator 5. 
Numerous characteristics, advantages, and embodiments of the invention have 
been described in detail in the foregoing description with reference to 
the accompanying drawings. However, the disclosure is illustrative only 
and the invention is not limited to the precise illustrated embodiments. 
Various changes and modifications may be effected therein by one skilled 
in the art without departing from the scope or spirit of the invention.