Refrigeration system including capacity modulation

A refrigeration system adapted particularly for a vehicle air conditioning system and including a capacity modulation mechanism. A portion of the liquid refrigerant at the outlet of the condenser is fed back to the suction chamber of the compressor through the orifice of a bypass valve. The valve is mounted on the compressor and is responsive to suction chamber pressure. As the evaporator temperature decreases, suction chamber pressure also decreases thereby opening the valve to meter a small amount of bypassed liquid refrigerant into the suction chamber of the compressor. A portion of the hot discharge gas may also be bypassed back into the suction chamber through the same valve that meters the bypassed liquid refrigerant.

BACKGROUND OF THE INVENTION 
The present invention relates to a refrigeration system and in particular 
to a refrigeration system and compressor wherein hot discharge gas and 
liquid refrigerant are bypassed to the suction side of the compressor in 
order to provide for modulation of cooling capacity. The refrigeration 
system is particularly adapted for use in a vehicle air conditioning 
system. 
In automotive air conditioning systems, if the ambient temperature is quite 
high, the air conditioner refrigeration system normally operates 
continuously in order to maintain the desired temperature within the 
vehicle. However, under cooler ambient temperature conditions, continuous 
operation of the compressor provides too much cooling capacity so that the 
temperature of the evaporator decreases below freezing and ice forms on 
the evaporator fins. Such undesirable freezing up of the evaporator is 
even more likely to occur under high humidity conditions. 
One known way to prevent evaporator freeze up and modulate the capacity of 
the refrigeration system is to cycle the compressor off when the 
evaporator becomes too cold. A disadvantage to this technique is that the 
repeated cycling on and off of the compressor is likely to produce 
accelerated wear of the clutch plates and other parts of the compressor 
due to the rapid acceleration of the compressor moving parts when the 
clutch plates are engaged. In vehicles with small engines there is a 
further disadvantage in that the intermittent loading and unloading of the 
engine as the compressor cycles on an off causes a noticeable variation in 
engine speed. 
Another prior art technique for modulating the capacity of the 
refrigeration system is to employ a compressor having variable 
displacement. In a swash plate compressor, the pitch of the swash plate 
can be varied to thereby change displacement. In multi-cylinder 
compressors, one or more cylinders can be blocked to thereby partially 
unload the compressor. However, the mechanisms for displacement variation 
are typically complicated and may require sophisticated controls. 
One known possibility is to bypass a portion of the discharge gas to the 
suction side of the compressor, but this normally causes a rise in the 
temperature of the compressor to unacceptably high levels. Another known 
possibility is to bypass a portion of the liquid to the suction side of 
the compressor in response to suction gas temperature in order to maintain 
a substantially constant predetermined super-heat of the suction gas 
entering the compressor. 
Although bypassing of liquid refrigerant from the condenser or hot 
discharge gas from the discharge side of the compressor will affect the 
capacity of the compressor, such prior art attempts at providing capacity 
control have not been effective in providing smooth control over the full 
range of ambient temperatures experienced by a vehicle air conditioning 
system. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, in one form thereof, a portion of 
the hot discharge gas from the discharge side of the compressor and a 
portion of the liquid refrigerant from the outlet side of the condenser 
are fed back to the suction chamber of the compressor. The bypassed 
discharge gas and liquid refrigerant are metered into the suction chamber 
of the compressor by means of a valve which is responsive to suction 
chamber pressure. Thus, both the discharge gas and liquid are metered into 
the suction cavity simultaneously and proportionately in response to 
suction cavity pressure. Because of the substantially higher pressure of 
the discharge gas, it is desirable that mixing of the bypassed discharge 
gas and liquid refrigerant not occur until the suction cavity, and for 
this reason, the two fluids are maintained segregated in the valve. 
In the preferred embodiment, positive pressure within the suction cavity 
maintains the bypass valve closed. However, when the evaporator 
temperature begins to decrease, suction pressure drops, and a return 
spring acting on the valve piston begins to open the valve thereby 
permitting hot gas and liquid refrigerant to be metered into the suction 
cavity. The injected liquid flashes in the compressor suction cavity. This 
results in an increase in evaporator pressure and temperature, thereby 
reducing the capacity of the compressor. The bypassed discharge gas lowers 
head pressure and reduces the compressor brake horsepower. As the pressure 
of the evaporator increases, this increases suction pressure thereby 
tending to close the bypass valve. Accordingly, the system is 
self-modulating and is capable of maintaining evaporator temperature 
essentially constant. By bypassing a portion of the liquid refrigerant 
around the evaporator, less refrigerant is available for extracting heat, 
thereby resulting in increased evaporator temperature. 
In a preferred form of the invention, the flow of bypassed refrigerant is 
restricted by an orifice in the valve on the suction side of the 
compressor so that the liquid flashes when it is discharged from the valve 
into the much larger expansion volume of the suction chamber. Since the 
bypassed discharge gas is not mixed with the bypass refrigerant until the 
liquid refrigerant and discharge gas both reach the suction chamber, vapor 
lock preventing bypassing of the liquid refrigerant will not occur. 
By combining both discharge gas bypass and liquid refrigerant bypass, it is 
possible to reduce the capacity of the refrigeration system to zero at a 
given minimum evaporator temperature. As the evaporator temperature rises, 
the bypass valve will meter less bypassed gas and liquid refrigerant into 
the compressor until the proper evaporator temperature is again achieved. 
The invention, in one form thereof, relates to a refrigeration system 
including capacity modulation and having a compressor including a suction 
chamber and a discharge side, a condenser having an inlet side connected 
to the discharge side of the compressor and an outlet side, and an 
evaporator connected between the outlet side of the condenser and the 
suction chamber of the compressor. A liquid bypass conduit is connected 
between the outlet side of the condenser and the suction chamber of the 
compressor for bypassing a portion of the liquid refrigerant from the 
condenser around the evaporator to the compressor suction chamber. A 
pressure responsive valve on the compressor having an inlet connected to 
the bypass conduit and an outlet opening into the suction chamber opens 
and closes in response to pressure in the suction chamber for the purpose 
of metering bypassed liquid refrigerant into the suction chamber to 
thereby vary the cooling capacity of the compressor. 
The refrigeration system of the invention, in accordance with another form 
thereof, comprises a liquid bypass conduit connected between the outlet 
side of the condenser and the suction side of the compressor to bypass a 
portion of the liquid refrigerant from the condenser around the evaporator 
to the suction side of the compressor. A pressure responsive valve is 
connected to the bypass conduit for metering the bypassed liquid 
refrigerant to the suction side of the compressor, the valve opening and 
closing in response to the pressure at the suction side of the compressor. 
The refrigeration system of the invention, in accordance with another form 
thereof, further comprises a hot discharge gas bypass passage connected to 
the discharge side of the compressor for bypassing a portion of the 
gaseous discharge refrigerant into the suction side of the compressor. A 
pressure responsive valve on the compressor has an inlet connected to the 
liquid bypass conduit and an outlet opening into the suction chamber and 
opens and closes in response to pressure in the suction chamber for 
metering bypassed liquid refrigerant into the suction chamber to thereby 
vary the capacity of the compressor. 
In accordance with one form of the invention, the valve has a second inlet 
connected to the discharge gas bypass passage and an outlet connected to 
the suction chamber for variably metering bypassed discharge gas into the 
suction chamber in response to a control parameter indicating a desired 
change in cooling capacity of the compressor. In a preferred form of the 
invention, the control parameter is the suction chamber pressure. 
The invention also relates to a refrigeration compressor including capacity 
modulation having a suction chamber and a discharge chamber. A pressure 
responsive valve has a liquid refrigerant bypass inlet and an outlet 
opening into the suction chamber. The valve opens and closes in response 
to the pressure in the suction chamber for metering bypassed liquid 
refrigerant into the suction chamber to thereby vary the cooling capacity 
of the compressor. A hot discharge gas bypass passage is connected between 
the discharge chamber and suction chamber for bypassing a portion of the 
discharge gas and mixing the bypassed gas with bypassed liquid refrigerant 
in the suction chamber. Preferably, the gas discharge passage is connected 
to the pressure responsive valve, which meters bypassed discharge gas in 
response to compressor suction pressure. 
An object of the present invention is to provide a refrigeration system 
including capacity modulation wherein the compressor can run continuously 
and the capacity is modulated by bypassing liquid refrigerant or liquid 
refrigerant and hot discharge gas. 
A further object of the present invention is to provide a capacity 
modulation system for a compressor which does not require a complicated 
control system or an electrical power source. 
Another object of the present invention is to provide a capacity varying 
mechanism for a refrigeration system that is self-modulating. 
Yet another object of the present invention is to provide a refrigeration 
system having a capacity modulation mechanism which is uncomplicated and 
comprises few moving parts, thereby enhancing reliability and reducing the 
occasion for maintenance.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring now to the drawings, and in particular to FIG. 7, the 
refrigeration system according to the present invention is shown 
schematically. The refrigeration system 10 comprises a high side 
compressor 12 having its discharge outlet 14 connected by a line 16 to 
condenser 18. Condenser 18 is connected by line 20 through expansion valve 
or capillary tube 22 to evaporator 24, the latter being connected by line 
26 to the suction inlet 28 of compressor 12. 
Bypass valve 30 has its outlet 32 connected to the suction chamber of 
compressor 12 and is responsive to the pressure therein to meter bypassed 
liquid refrigerant and bypassed hot discharge gas into the suction 
chamber. Liquid refrigerant bypass line 34 is connected from the outlet 
side of condenser 18 to one of the inlets of bypass valve 30, and hot 
discharge gas bypass line 100 is connected between discharge outlet 14 of 
compressor 12 and the other inlet of bypass valve 30. 
Referring now to FIGS. 1-6, the details of compressor 12 and the manner in 
which compressor 12 and the refrigeration system of FIG. 7 operates will 
be described. Compressor 12 is a split crankcase, radial scotch yoke 
vehicle compressor similar to that described in U.S. Pat. No. 4,358,251 
issued to the assignee of the present invention. Said patent is expressly 
incorporated herein by reference. Compressor 12 comprises a front housing 
half 38 and a rear housing half 40 which are hermetically joined together 
at seam 42 and enclose and support crankcase 44. Crankshaft 46 is received 
within crankcase 44 and is supported on needle bearings 48 received within 
main bearing portion 50 for rotation within crankcase 44. Yoke slide 52 is 
disposed around bearings 54 and eccentric portion 56 of crankshaft 46. Two 
pairs of opposing pistons 58, only one of which is illustrated, are 
positioned over yoke slide 52 and reciprocate within crankcase cylinders 
60 as crankshaft 46 rotates. Suction valves 62 are connected to the upper 
surfaces 64 of pistons 58 and open and close suction passages 66 as 
pistons 58 reciprocate. Discharge chamber 70 surrounds pistons 58 and 
communicates with discharge passage 72 through port 74. Crankcase 44 is 
sealed against rear housing by O-ring 82. 
Crankshaft 46 is driven by pulley and clutch assembly 76 mounted on the 
forward end of crankshaft 46. Pulley and clutch assembly 76 is 
substantially as shown in the aforementioned U.S. Pat. No. 4,358,251. 
Crankshaft 46 includes passages 84 and 86 to transmit a portion of the 
suction refrigerant to pulley and clutch mechanism 76 for lubricating and 
cooling thereof. Counterweight assembly 88 is connected to the face of 
crankcase 44 by screw 90, and includes an opening 92 in the face thereof 
for the passage of suction refrigerant into passage 84. 
Bypass valve 30 comprises a valve body 94 mounted to housing 40 and 
crankcase 44 by means of a plurality of screws 96 (FIG. 2). Valve body 94 
has discharge passage 72 formed therein and bypass passage 100 
intersecting discharge passage 72. A pressure relief valve 102 is 
connected to passage 100 and is set to open if excessively high discharge 
pressures occur. Suction inlet 28 is connected by suction passage 104 to 
suction chamber 106. Suction refrigerant, which is normally in the gaseous 
state, flows into crankshaft passage 84 through passage 92, and flows 
around the flange portion 108 of counterweight assembly 88, through 
openings 110 into suction chamber 112 on the suction side of pistons 58. 
Discharge passage 72 is sealed by O-ring 116 and suction chamber 106 is 
sealed by O-ring 118. 
Press fit within bore 120 of valve body 94 is valve cylinder 122, which is 
shown in greater detail in FIGS. 3 and 4. Cylinder 122 comprises a center 
bore 124 within which valve piston 126 (FIGS. 5 and 6) is slidably 
received. Valve cylinder 122 comprises a hot discharge gas inlet 128 that 
communicates with discharge passage 100, and further comprises a bypass 
liquid refrigerant inlet 130 that communicates with bypass refrigerant 
line 34 (FIG. 7) through bore 132 and fitting 134. 
Piston 126 (FIGS. 5 and 6) comprises a pair of segmented annuli 136 and 138 
sealed from each other and communicating respectively with outlet openings 
140 and 142. Piston 126 is slidably received within the bore 124 of valve 
cylinder 122, and the axial travel thereof is limited by snap rings 144 
and 146 received in grooves 148 and 150, respectively. 
Piston 126 is urged toward its open position in which openings 136 and 138 
are in register with valve cylinder orifices 128 and 130 by return spring 
150 seated within spring cup 152 of bellows assembly 153 connected to 
piston 126 by screw 154. Spring 150 is received within bellows 156 and 
held under compression by valve plug 158 threadedly connected to the cap 
portion 160 of the bellows assembly. Flexible bellows 156 is sealed to cup 
152 and cap 160, the latter being connected to portion 162 of valve body 
94 by snap ring 164. O-ring 166 seals cap portion 160 against valve body 
162. 
The interior of bellows 156 is vented to the atmosphere through passage 170 
in plug 158, and the chamber 172 on the exterior of bellows 156 is 
connected to suction pressure by four axial passages 176. Suction pressure 
acting on bellows 156 urges the piston toward the closed position against 
the force of spring 150. The compression force of spring 150 can be 
adjusted by turning plug 158, to thereby adjust the suction chamber 
pressure at which valve 30 will open. 
It is desirable that the bypassed liquid refrigerant from line 34 (FIG. 7) 
be metered through orifice 130 at the valve and then expand within suction 
chamber 106, where the refrigerant will flash to its gaseous state. In 
order to prevent the higher pressure discharge gas from blocking the flow 
of liquid refrigerant through inlet 130, discharge gas and bypassed liquid 
refrigerant are maintained segregated in valve 30 until they are 
discharged into suction chamber 106, at which point the liquid refrigerant 
will flash and mix with the bypassed discharge gas. Orifices 128 and 130 
for the discharge gas and bypassed liquid refrigerant, respectively, may 
have diameters of 0.080 inch, for example. 
The compressor 12 and refrigeration system 10 operates in the following 
manner. On start up, positive pressure is generated within suction chamber 
106, 112, which forces valve piston 126 to the left as viewed in FIG. 1 
against the force of spring 150. Refrigerant is pumped through condenser 
118, where it condenses, and is then evaporated through expansion valve or 
capillary 22 into evaporator 24 before being returned to suction chamber 
106, 112 by line 26. If ambient conditions are such that the evaporator 24 
begins to cool excessively, the pressure within suction chamber 106, 112 
will drop, thereby permitting valve piston 126 to move to the right and at 
least partially uncover orifices 128 and 130 connected to discharge gas 
bypass passage 100 and liquid bypass line 34. This will permit a portion 
of the discharge gas and liquid refrigerant to flow through openings 136, 
138 and 140, 142 into suction chamber 106 whereupon the bypassed liquid 
refrigerant will flash to its gaseous state and mix with the bypassed 
discharge gas. The bypassed refrigerant will mix with incoming refrigerant 
through suction inlet 28, flow through openings 110 into chamber 112 and 
be pumped into discharge chamber 170 through passages 66 past suction 
valves 62. 
The bypassing of the liquid refrigerant raises the pressure and temperature 
of evaporator 24. Furthermore, by bypassing the evaporator with a portion 
of the refrigerant, less refrigerant is available to extract heat from the 
ambient. The net result of this is an increase in the temperature of the 
evaporator, which will cause a concomitant increase in suction pressure, 
thereby urging valve piston 126 toward its closed position. Thus, the 
valve mechanism 130 is self-modulating, and by properly adjusting the 
force of spring 150, evaporator 24 can be maintained at a substantially 
constant temperature. 
It has been found that by mixing a portion of bypassed discharge gas with 
the bypassed liquid refrigerant, the capacity of compressor 112 can be 
reduced to zero at a given minimum evaporator temperature, for example 
25.degree. F. By bypassing both hot gas and liquid refrigerant, the 
evaporator temperature can be maintained above 32.degree. F., thereby 
preventing evaporator freeze-up. 
This results in reduced head temperatures and pressures thereby resulting 
in lower brake horsepower and a compressor which runs cooler and quieter. 
The compressor is able to run continuously with the capacity being 
self-modulated through the opening and closing of bypass valve 30. 
It is desirable that the liquid refrigerant be flashed within the 
compressor suction chamber 106 rather than prior to entering the 
compressor, and this is the reason that valve 130 is mounted directly to 
suction chamber 106. This also results in good mixing of bypassed 
discharge gas with bypassed liquid refrigerant, because the two will mix 
in their gaseous state subsequent to flashing of the bypassed liquid 
refrigerant. Although the invention has been described in terms of a 
refrigerant system for a vehicle air conditioner, in which application it 
is particularly advantageous, it can also be applied to other 
refrigeration systems. 
While this invention has been described as having a preferred design, it 
will be understood that it is capable of further modification. This 
application is, therefore, intended to cover any variations, uses, or 
adaptations of the invention following the general principles thereof and 
including such departures from the present disclosure as come within known 
or customary practice in the art to which this invention pertains and fall 
within the limits of the appended claims.