Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF T~ INVENTION
In au~omotive air conditioning sys~ems conditions
may arise causlng the "low side" (compressor intake) pressure
to rise to excessive levels which can damage the compressor.
To guard against this condition thermostatic expansion valves
have been provided with a low side pressure limit feature.
Excessive "high side" (compressor output) pressure can also
cause compressor damage. Normally the high side and low side
pressures tend to rise together and the low side pressure
limit will protect the compressor from overload. There are
some conditions, however, when the high side pressure is
excessive while the low side pressure is normal. To protect
against compressor overload in such cases the system is
usually provided with a pressure switch responding to exces-
sive high side pressure to disconnect the compressor clutch.
This stops all cooling, causes compressor belt wear, requires
additional wiring and conduit connections, and causes a
momentary drag on engine performance which can be felt in
small engine cars when the clutch re-engages.
SU~D~ARY OF THE IN~E~TION
:
The object of this invention is to protect against
excessive high side pressure in an automotive air condition-
ing system by modulating or throttling the flow to the
thermostatic expansion valve when the pressure rises to
excessive levels. When the flow to the thermostatic expan
sion valve is reduced, flow to and from the compressor is
reduced causing the high side pressure to fall.
2.
74~:
The evaporator pressure (thermostatic expansion
valve outlet pressure~ is relatively uniform within 207 kPa
in an automotive air conditioning system (during operation)
and the high side pressure is subject to much greater
variation. ~n a comparative basis the evaporator pressure
ma~ be considered uniform. With this in mind I provide a -
throttling valve responsive to the difference between high
side pressure and evaporator pressure to throttle flow to
the thermostatic expansion valve and the system~ If desire~,
the throttling valve can be made responsive to the difference
between high side pressure and either atmospheric pressure
or a fixed pressure. In all cases the throttling action
starves the system and causes reduction in compressor outpu~
which causes the high side pressure to fall back to the
desired range. By incorporating this valve in the thermo- -
static expansion valve no additional system connections are
- ~ required. Since the compressor continues to operate, cooling
continues and engine performance is unaffected. In the
illustrated embodiments the throttling is upstream o~ the
thermostatic expansion valve but it could be downstream. And
the throttling valve could be separate from the thermostatic -
expansion valve but this would be more costly to build and
install. The concept is shown in connection with two types `
of thermostatic expansion valves and from this it should be
clear that the invention is not limited to a particular type
of thermostatic expansion valve.
Broadly speaking, the present invention provides,
in an automotive air conditioning system having a compressor ~;~
delivering refrigerant to a thermostatic expansion valve -~
which regulates flow to an evaporator in accordance with the ~;
control temperature, the refrigerant flowing back to the
compressor from the evaporator, the improvement comprising,
a throttling valve mounted in the thermostatic expan~ion
~ 3 ~
. ., .,, . . . . .. ... . . . . .. ... ~ . ............... . . . .. . . . .
.
411 ~
valve body in series with the thermostatic expansion valve,
piston means connected to the throttling valve with one side
exposed to pressure upstream of both valves and its other
side exposed to pressure downstream of both valves to actuate
the throttling valve to reauce or interrupt refrigerant
flow and thereby reduce pressure upstream of both valves
when the pressure upstream of both valves is abnormally
high.
DESCRIPTION OF THE DRAWINGS
... . . . .. . .. ... ..
].0 Fig, 1 is a vertical section through a thermostatic
expansion valve in a schematic air conditioning system.
Fig. 2 is another modification.
3a ~
.;.. ~ ,., :
Fig. 3 is a section on line 3--3 in Fig. 1.
Fig. 4 is similar to Fig. 3 but shows an
arrangement in which the throttling valve is actuated in
response to high side pressure.
Fig. 5 shows another variant in which changes in
atmospheric pressure have no effect.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The lower portion of vaLve body 10 is provided with
inlet 12 and outlet 14 separated by a partition through which
port 16 is provided to supply refrigerant to the space below
the partition. Ball-type valve 18 cooperates with seat 20
to control flow from the inlet to the outlet. The ball is
centered on cage 22 which is urged in the valve closing direc-
tion by spring 24 compressed between the cage and carrier 26
threaded into the end of the valve body and adjustable to
change the spring force. The end of the valve body i~ sealed
by cap nut 28 and an O-ring.
Va~ve 18 is actuated by push pin 30 which, in turn,
is actuated by diaphragm rider pin 32 fixed to diaphragm pad
34 and having an end proiection projecting through the pad
and diaphragm 36 ~o communicate with head chamber 38. Pin 30
has a close sliding fit in bore 40 to minimize leakage along
this portion since any such leakage would constitute a bypass.
In the upper portion of the valve body there is a
return conduit including inlet 42 connected to the outlet of
the evaporator E while outlet 44 is connected to the inlet of
compressor C. It will be appreciated that, as usual, the out-
put of the compressor is fed into condenser K and thence to
receiver R which is conducted to the inlet 12 of the valve
body 10. Pressure within the return conduit can communicate
4.
~ ~ ~7 ~
with chamber 46 below the diaphragm through por~ 48 in ~he
upper wall of the valve body. From this it will be clear
that the tolerance between diaphragm rider pin 32 and the
upper wall is not of great concern since a little leakage
here wilL hurt nothing. Diaphragm 36 is mounted between
domed head 54 and support cup 50 threaded in~o the upper end
of the valve body and sealed with respect thereto by means
of O-ring 52. Head chamber 38 is charged with a temperature
responsive charge through capillary tube 56 which is then
seaLed off.
It will be noted that rider pin 32 is provided with
a blind hole 58 which terminates approximately at the mid-
point of the ret~rn flow path through the upper portion of
the val~e body. The blind hole, in effect, provides a small
temperature sensing chamber 60 inside the rider pin and
located in the system return path. Pin chamber 60 will
always be col.der than head ch~mber 38 and, therefore, the
refrigerant charge will tend to condense in chamber 60 and
the control poin~ will be at ~his point which is ideally ~it-
uated. Since there is not much mass involved in the riderpin the response of the valve as thus far described would be
quite rapid and subject to fluctuation on any transient tem-
perature changes. This, of course, would result in hunting.
To damp out the hunting effect low conductivity sleeve 62 is
mounted over the rider pin where the pin passes through the
return flow path. This sleeve can wel~ be Delrin which, in
" \ ~ addition to low thermal conductivity, provides a self-
lubricating factor to insure free mo~ement of the rider 32.
The thickness determines the degree of damping.
In order to make the valve mountable in all
positions capil1ary restrictor 64 is fitted in the upper end
5.
~ ~7 ~ 2
of the rider pin. This, then, provides a very small
capillary hole connecting rider pin chamber 60 to head cham-
ber 38. This is adequate for transfer of pressure changes
but wilL minimize migration of any condensed rerigerant
charge in chamber 60 to the head chamber should the valve be
mounted upside down. Without this restrictor there could be
such migration wi~h the result tha~ the liquid refrigerant
migrating to the head chamber (which is warmer) would flash
to a gas ,~increasing the presswre) and ~hen promp~ly be
recondensed in chamber 60. This, of course, would induc~
hunting in the system. With the restrictor the hunting is
minimized.
As described to this point the thermostatic
expansion va~ve is the same as in U.S. Patent 3,537,645. The
present arrangement differs in provision of throttling valve
66 in cross bore 68 and carried by piston 70 in bore 72. The
end of bore 72 is cLosed by co~er 74 secured to body 10 by
screws 76 and sealed by 0-ring 78. The cover 74 provides a
seat for compressed spring 80 which urges the piston towards
the inLet with the maximum travel determined by plug valve 66
engaging the end of the bore 68. Conduit 82 leads from bore
72 to outlet 14 so the "back" of piston 70 is exposed to the
outlet (evaporator) pressure while the face of the piston
senses inlet ~high side~ pressure. When the pressure differ-
ential can overcome the spring load, the piston will move to
move the plug valYe across the inlet. This throttles flow to
the thermostatic expansion valve and the system causing
reduced fLow to and from the compressor which causes the high
side pressure to drop.
In the second modification (Fig. 2) the
thermostatic expansion valve configuration is more of the
6.
"normaL" type and the throttling valve is coaxial with theexpansion valve. Thus the thermos~atic expansion valve body
84 has an inLe~ 86 (provided with strainer 88) leading to
central partition 90. The valve body is provided with bore
92 intersecting the inlet and communicating wi~h the outlet
94. Valve 96 normally con~rols flow -Erom the inlet to the
outlet since the central aperture 98 is normally closed by
piston 100 biased upwardly by spring 102 carried in cup 104
Eixed on the valve support 106. Adjustable seat 108 threaded
in outlet 94 determines the load applied to spring 110 urging
the val~e 96 to its seat. Valve 96 is actuated by diaphragm
112 through push pin(s) 114. The diaphragm is fixed between
upper and lower head stampings 116~118 which are welded
together. Outlet pressure acts on the underside of the dia-
phragm through the clearance around the push pins. The space
above the diaphragm is connected to ~he conventional feeler
bulb 120 by capillary tube 122 and this closed system is
charged with a temperature responsive charge. Operation of
the thermostatic expansion valve is con~entional.
Piston 1~0 is provided with a stem projec~ing
through bore 98 with a plug valve 124 threaded on its upper
end and normally not restricting fLow. Inlet ~high side)
pressure acts on the top of the plug/stem. Outlet pressure
(evaporator pressure) acts on the bottom of the piston 100.
When the pressure differential exceeds the force of spring
lQ2, the piston moves down relative to the expansion valve 96
(which will be open) and the chamfered lower end oE plug 124
will cooperate with the seat to throttle flow and reduce the
high side pressure as in the first embodiment.
In Fig. 4 the throttling valve 166 is moun~ed in
-~ cross bore L68 and carried by piston 170 in bore 172 in a
. .. , .. . . ., " . . . - --
. ~, . , ~ . - , . - ... . ~
~ ~ ~ 7 ~ ~
ma~ner similar ~o the first embodiment. In this case,
however, the valve is to respond to the difference between
high side pressure and atmospheric pressure. Therefore,
piston 170 is carried by bellows 174 which is sealed to
shoulder 176 in cylinder 178 threaded into the valve body 10.
The end of the cylinder 178 is closed by disc 180. The disc
is ported a~ 182 to expose the interior of the bellows to
atmospheric pressure. Compressed spring 184 seats on the
disc and the piston 170 to establish the desired pre-load.
With this arrangement the high side pressure is opposed by
the spring force and atmospheric pressure. The total oppos-
ing force is generally considered as referenced from
atmospheric pressure which is more constant than evaporator
pressure~ Therefore, the pressure at which the valve starts
to throttle is more definite.
Fig. 5 shows the manner in which the high side
pressure alone determines ~he response pressure . . . . i.e.
the effect of atmospheric variation is e~iminated. This is
done by changing the end disc in cylinder 178 to a non-vented
disc 186 having a eapillary tube 188 which is used to evacu-
ate the interior of the bellows 174 and is then sealed.
Thereore, the high side pressure is opposed only by the
fixed force (pressure) of the spring 184 and the response
pressure is fixed.
As mentioned above, the throttling valve can, if
d~sired, be located downstream of the thermostatic expansion
valve by suitable porting inside the valve body. In some
cases this can be advantageous in that the throttling valve
is then controlling a 2-phase (liquid and vapor) refrigerant
and it is easier to close off flow. Where inadequa~e closure
: ., . - . ~.......... . . . - . . .-
. . .. . . . . . - . . .
~ 2
is obtained upstream, the extra cost (by reason of porting
and seals) of locating the valve downstream can be justified.
8`~
