U.S. patent application number 10/078201 was filed with the patent office on 2002-08-22 for air conditioners suitable for vehicles and methods for operating such air conditioners.
This patent application is currently assigned to Kabushiki Kaisha Toyota Jidoshokki. Invention is credited to Gennami, Hiroyuki, Kawaguchi, Masahiro, Kimura, Kazuya, Kuroki, Kazuhiro, Matsubara, Ryo, Suitou, Ken.
Application Number | 20020112492 10/078201 |
Document ID | / |
Family ID | 18906049 |
Filed Date | 2002-08-22 |
United States Patent
Application |
20020112492 |
Kind Code |
A1 |
Suitou, Ken ; et
al. |
August 22, 2002 |
Air conditioners suitable for vehicles and methods for operating
such air conditioners
Abstract
An air conditioner (1) includes an air conditioning circuit (2)
in which a cooling medium circulates. An electrically powered
compressor (C) is disposed within the air conditioning circuit (2)
for compressing the cooling medium and discharging the cooling
medium under high pressure. A refrigerant superheat feedback device
(22) adjusts the superheat condition of the cooling medium that is
returned to the compressor (C) for compression in order to ensure
an adequate supply of lubrication oil to the compressor (C).
Inventors: |
Suitou, Ken; (Kariya-shi,
JP) ; Kimura, Kazuya; (Kariya-shi, JP) ;
Kawaguchi, Masahiro; (Kariya-shi, JP) ; Kuroki,
Kazuhiro; (Kariya-shi, JP) ; Gennami, Hiroyuki;
(Kariya-shi, JP) ; Matsubara, Ryo; (Kariya-shi,
JP) |
Correspondence
Address: |
WOODCOCK WASHBURN KURTZ
MACKIEWICZ & NORRIS LLP
One Liberty Place - 46th Floor
Philadelphia
PA
19103
US
|
Assignee: |
Kabushiki Kaisha Toyota
Jidoshokki
|
Family ID: |
18906049 |
Appl. No.: |
10/078201 |
Filed: |
February 19, 2002 |
Current U.S.
Class: |
62/225 ;
62/84 |
Current CPC
Class: |
F25B 41/335 20210101;
F25B 2600/021 20130101; B60H 1/3205 20130101; F25B 49/025 20130101;
F25B 31/004 20130101; B60H 1/3214 20130101; F25B 27/00 20130101;
B60H 2001/3255 20130101; B60H 2001/3248 20130101; B60H 2001/3292
20130101; B60H 1/3222 20130101; B60H 2001/3285 20130101 |
Class at
Publication: |
62/225 ;
62/84 |
International
Class: |
F25B 043/02; F25B
041/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 20, 2001 |
JP |
2001-043975 |
Claims
1. An air conditioner comprising: an air conditioning circuit
comprising a circulating cooling medium and lubricating oil, an
electrically powered compressor disposed within the air
conditioning circuit, the compressor being arranged and constructed
to compress the cooling medium and discharge the cooling medium
under high pressure, and a refrigerant superheat feedback device
arranged and constructed to adjust the superheat condition of the
cooling medium that is returned to the compressor in order to
ensure an adequate supply of lubrication oil to the compressor
during a low load operation.
2. An air conditioner as in claim 1, wherein the refrigerant
superheat feedback device comprises an expansion valve.
3. A method for compressing a cooling medium using an air
conditioner that includes an electrically-driven compressor, which
is arranged and constructed to compress the cooling medium and
discharge the cooling medium under high pressure, comprising:
adjusting the superheat condition of the cooling medium that is
returned to the compressor in response to a load that is applied to
the air conditioner.
4. A method as in claim 3, wherein the change of the cooling medium
temperature is performed by an expansion valve.
5. An air conditioner comprising: an air conditioning circuit
comprising a circulating cooling medium and lubricating oil, an
electrically driven compressor disposed within the air conditioning
circuit, the compressor being arranged and constructed to compress
the cooling medium and discharge the cooling medium under high
pressure, and a controller arranged and constructed to control the
phase state of the cooling medium within the air conditioning
circuit, wherein the controller causes the cooling medium supplied
to an inlet of the compressor to be in dual-phase, gas-liquid state
when an operating load on the air conditioner is relatively
low.
6. An air conditioner as in claim 5, further including an
evaporator disposed on an upstream side of the compressor and
within the air conditioning circuit, wherein the controller is
further arranged and constructed to control the flow of the cooling
medium at an inlet of the evaporator.
7. An air conditioner as in claim 6, wherein the controller
controls the flow of the cooling medium at the inlet of the
evaporator based upon the superheat condition of the cooling medium
at the outlet of the evaporator.
8. An air conditioner as in claim 6, wherein the controller
comprises a thermosensitive cylinder disposed proximal to the air
conditioning circuit downstream of the evaporator and communicating
with a first side of a movable diaphragm, and the air conditioning
circuit communication with a second side of the movable diaphragm,
the movable diaphragm being coupled an expansion valve disposed
upstream of the evaporator, the thermosensitive cylinder containing
a gaseous composition that is different from the cooling medium,
wherein the expansion valve is arranged and constructed to control
the flow of the cooling medium into the inlet of the evaporator
based upon differences between the pressure of the cooling medium
at the outlet of the evaporator and the pressure of the gaseous
composition within the thermosensitive cylinder.
9. An air conditioner as in claim 6, wherein the controller
comprises a cross-charge expansion valve.
10. An apparatus suitable for circulating cooling medium and
lubrication oil to an electrically powered compressor within an air
control circuit of an air conditioner, comprising: a controller
arranged and constructed to control the phase state of the cooling
medium in the air conditioning circuit to as to supply a dual-state
gas liquid cooling medium to an inlet of the compressor during
operation of the air conditioner under a low load.
11. An apparatus as in claim 10, further comprising an evaporator
disposed on an upstream side of the compressor and within the air
conditioning circuit, wherein the controller is arranged and
constructed to control the flow of the cooling medium into an inlet
of the evaporator.
12. An apparatus as in claim 11, wherein the controller is further
arranged and constructed to control the flow of the cooling medium
into the inlet of the evaporator based upon the superheat condition
of the cooling medium exiting an outlet of the evaporator.
13. An apparatus as in claim 12, wherein the controller comprises a
cross-charge expansion valve for controlling the flow of cooling
medium into the inlet of the evaporator.
14. A method for circulating a refrigerant and lubrication oil
within an air conditioning circuit of an air conditioner including
an electrically powered compressor, comprising: supplying the
lubrication oil to the compressor within a dual-state gas-liquid
cooling medium when the load on the air conditioner is relatively
low.
15. A method as in claim 14, further comprising controlling the
phase state of the cooling medium at an inlet of the compressor
based upon the pressure at an inlet of an evaporator that is
disposed on an upstream side of the compressor within the air
conditioning circuit.
16. An air conditioner comprising: an electrically powered
compressor arranged and constructed to compress a refrigerant and
discharge the refrigerant under higher pressure, the refrigerant
comprising lubricating oil for lubricating parts within the
compressor, a condenser receiving the refrigerant from the
compressor, an expansion valve receiving refrigerant from the
condenser, an evaporator receiving refrigerant from the expansion
valve, and means for adjusting the amount of refrigerant supplied
to evaporator in order to adjust the phase state of the refrigerant
that is returned to the compressor, thereby ensuring an adequate
supply of lubrication oil to the compressor during a low load
operation.
17. An air conditioner as in claim 16, wherein the adjusting means
contains a gas having a different composition from the refrigerant
and the adjusting means is disposed proximal to an outlet port of
the evaporator, wherein the gas within the adjusting means is
physically isolated from the refrigerant, but assumes the same
temperature as the refrigerant exiting the outlet port of the
evaporator.
18. An air conditioner as in claim 17, wherein the adjusting means
further comprises a movable diaphragm coupled to the expansion
valve, wherein the gas within the adjusting means communicates with
a first side of the movable diaphragm and the refrigerant exiting
from the outlet port of the evaporator communicates with a second
side of the movable diaphragm, wherein changes in the relative
pressures of the gas and refrigerant cause the movable diaphragm to
move and adjust the amount of refrigerant supplied to the
evaporator by the expansion valve.
19. An air conditioner as in claim 18, wherein the adjusting means
adjusts the phase state of the refrigerant returning to the
compressor to be a substantially gas-liquid phase state when the
compressor is operating under a relatively low load.
20. A apparatus for circulating a refrigerant and lubrication oil
within an air conditioning circuit of an air conditioner including
an electrically powered compressor, comprising: means for supplying
the lubrication oil to the compressor within a dual-state
gas-liquid cooling medium when the load on the air conditioner is
relatively low in order to ensure reliable lubrication of the
compressor.
Description
[0001] This application claims priority to Japanese application
serial number 2001-43975, which application is hereby incorporated
by reference herein in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to air conditioners for
vehicles and methods for operating such air conditioners. In
particular, the present invention relates to air controlling
techniques in such air conditioners that have an air control
circuit and a compressor, preferably an electrically driven
compressor, for circulating a cooling medium or refrigerant within
the air control circuit.
[0004] 2. Description of the Related Art
[0005] Generally speaking, known air conditioning compressors are
mechanically driven by means of a belt coupled to the engine, as in
U.S. Pat. No. 5,813,249. However, electrically driven compressors
have been proposed for use as air conditioner compressors, because
the rotational speed of the electric motor can be controlled
independently of the rotational speed of the engine.
[0006] In addition, lubrication oil is typically utilized in order
to lubricate sliding parts within the compressor. As a result,
lubrication oil recovering devices are usually disposed within the
compressor in order to recover the lubrication oil and prevent the
lubrication oil from flowing out of the compressor housing into the
air conditioning circuit (e.g., into the condenser and evaporator).
However, incorporation of such lubrication oil recovering devices
increases the manufacturing costs and size of such compressors and
thus, elimination of such lubrication oil recovering devices would
be advantageous.
SUMMARY OF THE INVENTION
[0007] It is, accordingly, one object of the present invention to
teach improved air conditioners that utilize compressors that do
not require lubrication oil recovering devices. Therefore,
manufacturing costs of such air conditioners can be reduced, and
the size of the compressors can be minimized.
[0008] In one aspect of the present teachings, air conditioners are
taught that include an air conditioning circuit in which a cooling
medium circulates. A compressor may be disposed within the air
conditioning circuit and preferably serves to compress the cooling
medium and discharge the cooling medium under higher pressure.
Thus, the compressed cooling medium can then be expanded, e.g., in
an evaporator, in order to cool a flow of air that will be supplied
to the vehicle interior. Preferably, the compressor may comprise an
electrically driven motor that drives the compressor. A refrigerant
superheat feedback device may preferably vary the degree of
superheat or the superheat condition of the cooling medium that is
returned to the compressor. For example, a superheat monitoring
device may be disposed downstream of an evaporator in order to
monitor the superheat condition of the cooling medium that is being
returned to the compressor for compression. Based upon the detected
superheat condition of the cooling medium downstream of the
evaporator, the flow of cooling medium into the evaporator can be
appropriately adjusted, as will be discussed further below.
[0009] According to the present specification, the term "superheat"
or "degree of superheat" is intended to mean the difference
(usually, measured in degrees of Celsius or Fahrenheit) between the
actual temperature of the cooling medium (refrigerant), which
actual temperature is measured at a certain pressure, and the
saturation temperature of the cooling medium (refrigerant) at that
same pressure. In other words, the degree of superheat of the
cooling medium (refrigerant) may be expressed as the difference
between the vapor point of the cooling medium at a certain pressure
(i.e., the temperature at which the cooling medium evaporates at a
given pressure) and the actual temperature of the cooling medium
exiting the evaporator. Thus, if the cooling medium (refrigerant)
is at a higher temperature when exiting the condenser than the
vapor saturation temperature for the pressure at which the cooling
medium is exiting the condenser, the difference is called the
degree of superheat or the superheat condition of the cooling
medium (refrigerant).
[0010] Therefore, the refrigerant superheat feedback device may
effectively control the superheat condition of the cooling medium
that is being supplied to the compressor. For example, at
relatively low pressures and high temperatures, the cooling medium
is substantially in a gaseous state. On the other hand, at
relatively high pressures and low temperatures, the cooling medium
is substantially in a liquid state. Naturally, at intermediate
pressures and temperatures, the cooling medium may be in a
substantially dual-phase gas-liquid state.
[0011] In one representative embodiment, the refrigerant superheat
feedback device can adjust the superheat condition of the cooling
medium, so that the cooling medium exiting the evaporator is in a
dual-phase state. In that case, the liquid phase of the cooling
medium can effectively convey lubrication oil into the compressor
and reliably lubricate sliding parts within the compressor. Thus,
if the cooling medium can be effectively maintained in a state that
will ensure effective lubrication of the compressor regardless of
the workload on the compressor, the air conditioner will not
require a costly lubrication oil recovering device. In addition,
the air conditioner may have a relatively simple construction as
compared to known air conditioning systems.
[0012] Thus, the inventors have found that the lubrication oil that
flows out from the compressor can still be used to lubricating part
within the compressor without incorporating lubrication oil
recovering devices, if the lubrication oil adequately circulates
within the air conditioning circuit and returns to the compressor.
In order to effectively circulate the lubrication oil, the cooling
medium may serve as a carrier for the lubrication oil. The ability
of the cooling medium to serve as a carrier for the lubrication oil
may be improved by controlling the degree of superheat of the
cooling medium. For example, saturated cooling medium having a
liquid phase of the cooling medium may effectively convey the
lubrication oil even if the flow rate of the cooling medium is
relatively small, which may occur in a low load operation for the
air conditioning system. On the other hand, if the compressor is
operating under a relatively high load, the flow rate of the
lubrication oil through the air conditioning system will be
relatively high. In that case, an adequate amount of lubricating
oil will be returned to the compressor, even if the cooling medium
is substantially in a gaseous state (i.e., the cooling medium
returning to the compressor contains little or no liquid cooling
medium).
[0013] In another aspect of the present teachings, methods for
operating air conditioners are taught that include adjusting the
superheat condition of the cooling medium that is supplied to the
compressor in response to the load that is applied to the air
conditioner. Therefore, if the superheat condition of the cooling
medium, which is supplied to the compressor, is adjusted in
response to the load that is applied to the air conditioner, the
cooling medium may be brought into a dual-phase state, which
includes a liquid phase of the cooling medium, in order to more
effectively convey the lubrication oil within the air conditioning
system.
[0014] Other objects, features and advantages of the present
invention will be readily understood after reading the following
detailed description together with the accompanying drawings and
the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a schematic diagram of a representative air
conditioner;
[0016] FIG. 2 shows a representative cross-charge expansion valve
and associated parts;
[0017] FIG. 3 shows the relationship between valve lift and the
flow rate of cooling medium (refrigerant) compared to the enthalpy
of the cooling medium (refrigerant);
[0018] FIG. 4 is a graph showing the relationship between
temperature T(12) and pressure P(12) at an outlet of an evaporator
of the air conditioner when a representative expansion valve is
incorporated; and
[0019] FIG. 5 is a Mollier chart for a cooling medium circulation
process of the air controlling circuit.
DETAILED DESCRIPTION OF THE INVENTION
[0020] In one embodiment of the present teachings, the refrigerant
superheat feedback device may vary the state (e.g., dual-phase
state or substantially gaseous state) of the cooling medium that
returns to the compressor during the circulating process in
response to the load applied to the air conditioner (e.g., the
compressor) during the air conditioning operation. The refrigerant
superheat feedback device preferably performs two functions: (1)
monitoring the superheat condition (e.g., the enthalpy) of the
cooling medium that is exhausted from an evaporator and which
cooling medium will be supplied to the compressor and (2) adjusting
the flow of cooling medium into the evaporator in order to maintain
an appropriate state of the cooling medium that is exhausted from
the evaporator.
[0021] For example, if a high load is being applied to the air
conditioning system, the cooling medium that is being exhausted
from the evaporator may be maintained in a substantially gaseous
state, thereby transferring the maximum amount of cooling energy to
a flow of air that will be supplied to the vehicle interior. In
this case, because the flow rate of the cooling medium within the
air conditioning system is relatively high, sufficient lubricating
oil will be circulated to the compressor in order to reliably
lubricate the compressor parts, even though the cooling medium is
substantially in a gaseous state.
[0022] On the other hand, if the load on the air conditioning
system is relatively low, the flow rate of the cooling medium
within the air conditioning systems also may be relatively low.
Because gaseous cooling medium is less effective for conveying
lubricating oil than liquid cooling medium, the compressor may not
be adequately lubricated if only gaseous cooling medium is being
supplied to the compressor in a low load operation. Therefore, the
superheat state of the cooling medium exiting the evaporator can be
adjusted by changing the flow of cooling medium into the evaporator
in order to ensure that dual-phase cooling medium is exhausted from
the evaporator and is conveyed to the compressor during a low load
operation.
[0023] Because the dual-phase cooling medium includes a liquid
phase that can effectively convey the lubricating oil, adequate
lubrication of the compressor can be ensured, even in low load
operations. Consequently, it is not necessary to utilize a
lubricating oil recovery device within the air conditioning system,
because an adequate supply of lubricating oil to the compressor is
ensured during all types of workload on the air conditioning system
(i.e., the compressor).
[0024] In one representative embodiment, the refrigerant superheat
feedback device may include a control valve disposed within the air
control circuit, or any other type of controller, that is coupled
to the air conditioning circuit but is physically isolated from the
cooling medium within the air conditioning circuit. For example, an
expansion valve may be utilized to control the flow rate of the
cooling medium in response to changes in the load applied to the
air conditioning system. Alternatively, the refrigerant superheat
feedback device may be a separate control valve. Also, the
combination of these valves may be used.
[0025] In addition, the refrigerant superheat feedback device may
include a device that monitors the superheat condition of the
cooling medium exiting the evaporator and adjusts the flow rate of
cooling medium into the evaporator. For example, in one
representative embodiment, a cross-charge type expansion valve may
be utilized for this purpose. Generally speaking, such a device
includes two features.
[0026] First, a means for monitoring the temperature of the cooling
medium is provided. For example, a substantially sealed volume of
gas, which gas preferably has a composition that differs from the
cooling medium, may be disposed substantially adjacent to the
portion of the air conditioning circuit containing the cooling
medium that has been exhausted from the evaporator. Thus, because
this gas is physically isolated from the cooling medium, but is
disposed in a manner so as to have substantially the same
temperature as the cooling medium, the gas will expand and contract
as the temperature of the cooling medium respectively increases and
decreases.
[0027] Second, a means for monitoring the pressure of the cooling
medium also is preferably provided. For example, a movable
diaphragm may separate the cooling medium within the air
conditioning system and the gas within means for monitoring the
temperature of the cooling medium. Thus, as the relatively
pressures of the gas and the cooling medium change, the diaphragm
will change position. If the diaphragm is coupled to the expansion
valve, the change in position of the diaphragm will change the
opening degree of the expansion valve. Therefore, the superheat
condition of the cooling medium that is being exhausted by the
evaporator is reflected by the position of the diaphragm. Further,
the position of the diaphragm determines the flow rate of the
cooling medium into evaporator.
[0028] Consequently, the superheat condition of the cooling medium
that is exiting the evaporator can be effectively "fed back" to the
expansion valve in order to control the opening degree of the
expansion valve. Thus, the flow rate of the cooling medium into the
evaporator also can be effectively controlled in order to maintain
the state of the cooling medium that is exiting the evaporator in a
condition that will effectively convey sufficient lubricating oil
to the compressor and ensure adequate lubrication of the
compressor.
[0029] In another representative embodiment, when the load on the
air conditioning system is relatively low and the flow rate of
circulating cooling medium is relatively small, the refrigerant
superheat feedback device may decrease the superheat condition
(e.g., enthalpy) of the cooling medium that is supplied to the
compressor. In this case, the gaseous cooling medium may be brought
into a dual-phase state that includes a liquid phase. Therefore,
the lubrication oil may be conveyed by the liquid phase of the
cooling medium so as to reliably circulate and return to the
compressor. As a result, the lubrication of parts within the
compressor may be reliably maintained, and the durability of the
compressor may be improved.
[0030] Thus, the lubrication oil can be effectively circulated in a
cost-effective and simple manner by incorporating such a
refrigerant superheat feedback device and the air conditioner will
not require a costly lubrication oil recovering device.
[0031] In another representative embodiment, the refrigerant
superheat feedback device, which may include an expansion valve,
may serve to cause the cooling medium that is being returned to the
compressor to be substantially a vapor (i.e., substantially gaseous
state) when the load applied to the air conditioner is high and the
flow rate of circulating cooling medium is relatively large. On the
other hand, when the load applied to the air conditioner is low and
the flow rate of circulating cooling medium is relatively small,
the expansion valve may serve to cause the cooling medium that is
being returned to the compressor to be dual-phase (i.e.,
gas-liquid).
[0032] Therefore, when the load applied to the air conditioner is
high and the flow rate of circulating cooling medium is relatively
large, the superheat condition of the cooling medium may be
increased, which will cause the cooling medium to be in a
substantially gaseous state. However, because the flow rate of the
gaseous cooling medium is relatively large, the lubrication oil
still may reliably flow together with the cooling medium.
Therefore, the lubrication oil will smoothly and adequately
circulate within the air control circuit.
[0033] As a result, the lubrication oil can be effectively
circulated in a cost-effective and simple manner by incorporating a
refrigerant superheat feedback device having the above features and
the air conditioner does not require a costly lubrication oil
recovering device. Furthermore, the compressor can be effectively
operated regardless of the workload on the air conditioning
system.
[0034] In another representative embodiment, methods for operating
an air conditioner are taught that may include adjusting the
superheat condition of the cooling medium in response to a load
that is applied to the air conditioner. For example, if the load
applied to the air conditioner is low and the flow rate of
circulating cooling medium is relatively small, the superheat
condition of the cooling medium, which is being returned to the
compressor, may be controlled such that the cooling medium is
brought to a dual-phase state.
[0035] In that case, the vapor of the cooling medium will partially
liquefied. As a result, even if the lubrication oil within the
compressor flows into the air control circuit when the load applied
to the air conditioner is low and the flow rate of circulating
cooling medium is small, the lubrication oil may flow together with
the liquefied phase of the vapor and then may return to the
compressor. Consequently, the lubrication oil can be effective
circulated in a cost-effective and simple manner.
[0036] Each of the additional features and method steps disclosed
above and below may be utilized separately or in conjunction with
other features and method steps to provide improved air
conditioners and methods for designing and using such air
conditioners. Representative examples of the present invention,
which examples utilize many of these additional features and method
steps in conjunction, will now be described in detail with
reference to the attached drawings. This detailed description is
merely intended to teach a person of skill in the art further
details for practicing preferred aspects of the present teachings
and is not intended to limit the scope of the invention. Only the
claims define the scope of the claimed invention. Therefore,
combinations of features and steps disclosed in the following
detail description may not be necessary to practice the invention
in the broadest sense, and are instead taught merely to
particularly describe representative examples of the invention.
[0037] A representative embodiment of an air conditioner will now
be described with reference to the drawings. A schematic diagram of
the general configuration of a representative air conditioner 1 is
shown in FIG. 1. The air conditioner 1 may include an air
controlling circuit 2 that serves to circulate cooling medium or
refrigerant. An electrically driven compressor C, a condenser 10,
an evaporator 12, a receiver 14 and an expansion valve 20 may be
disposed within the air controlling circuit 2. The compressor C
preferably serves to compress a gaseous, or substantially gaseous,
cooling medium and discharge pressurized cooling medium. An
inverter I may be included to selectively power an electric motor M
that drives the compressor C. In one preferred embodiment, the
compressor C may be a scroll-type compressor.
[0038] A vehicle engine E may serve as the drive source of a
vehicle and may be mechanically connected to an alternator O, e.g.,
by a belt or another transmission means. The alternator O may be
electrically connected to a battery B and also to the inverter I.
Therefore, electric current generated by the alternator O may be
utilized to drive the motor M or may charge the battery B.
[0039] The expansion valve 20 preferably serves as a pressure
reducer or regulator by rapidly expanding the relatively high
temperature, high-pressure liquid refrigerant supplied by the
condenser 10. By passing the liquid refrigerant, e.g., through a
small opening (not shown) in the expansion valve 20, a relatively
low temperature, low-pressure gas-liquid two-phased atomized
refrigerant may be generated.
[0040] A thermosensitive cylinder or element 22 may be utilized to
essentially "feedback" the superheat condition of the cooling
medium at the exhaust port of the evaporator 12 to the evaporation
valve 20 in order to control the supply of refrigerant to
evaporator 12. The thermosensitive cylinder 22 preferably contains
a gaseous composition that is different from the cooling medium or
refrigerant that is disposed within the air conditioning circuit 2.
Moreover, the gas within the thermosensitive cylinder 22 is
preferably isolated from the refrigerant within the air
conditioning circuit 2. In other words, the thermosensitive
cylinder 22 is disposed so as to adjoin or substantially contact
the portion of the air conditioning circuit 2 containing the
refrigerant that has been exhausted from the evaporator 12.
However, the gas within the thermosensitive cylinder 22 and the
refrigerant within the air conditioning circuit 2 remain separated.
Therefore, the thermosensitive cylinder 22 may serve as a
refrigerant temperature detector that detects the temperature of
the gaseous refrigerant that is being fed into the compressor C
after having been exhausted from the evaporator 12. In order words,
the gas within the thermosensitive cylinder 22 preferably assumes
the same temperature as the cooling medium exiting the evaporator
12, due to the proximal relationship of the thermosensitive
cylinder 22 and the air conditioning circuit 2.
[0041] Referring to FIG. 2, the expansion valve 20 may be a
cross-charge expansion valve and may include a throttle valve 21
that is disposed at the inlet of the expansion valve 20. A spring
23 may bias the throttle valve 21. Further, the throttle valve 21
may connected to a diaphragm 25 that is disposed within a diaphragm
chamber 27. A first side of the diaphragm chamber 27 may
communicate with the thermosensitive cylinder 22 via a first tube
29 (i.e., the gas within the thermosensitive cylinder 22 applies
pressure to the first side of the diaphragm 25). A second side of
the diaphragm chamber 27 may communicate with the outlet side of
the evaporator 12 via a second tube 31 (i.e., the cooling medium
within the air conditioning circuit 2 applies pressure to the
second side of the diaphragm 25). As a result, the position of the
throttle valve 21 (i.e., the degree of opening) will vary in
response to differences between the pressure within the first tube
29 and the pressure within the second tube 31, which differences
will affect the relative position of the diaphragm 25.
[0042] In other words, the second tube 31 is disposed in a way that
it circumvents the evaporator 12 and forms a pressure guiding
passage which connects the interior of the thermosensitive cylinder
22 with the interior of a pressure chamber provided at one side of
the diaphragm 25. The first tube 29 serves as pressure
communication unit for communicating pressure changes within the
thermosensitive cylinder 22 to the pressure chamber provided at the
other side of the diaphragm 25.
[0043] Preferably, activated carbon CA may be contained within the
thermosensitive cylinder 22. As noted above, in a cross-charge
expansion valve, the gas disposed within the thermosensitive
cylinder 22 is different in kind or composition from the
refrigerant flowing through the air controlling circuit 2. However,
this different gas is sealed within a channel that connects the
diaphragm chamber 27 and the thermosensitive cylinder 22, as
discussed above. The gas within this channel is chosen such that at
least some of the gas is absorbed by the activated carbon CA in
order to provide a reservoir of gas for expansion, when the
temperature of the cooling medium that is being discharged from the
evaporator 12 increases.
[0044] The thermosensitive cylinder 22 may be attached to the
outlet of the evaporator 12, so that the pressure within the
thermosensitive cylinder 22, as well as the pressure within the
first tube 29, varies in response to the superheat condition of the
refrigerant at the outlet of the evaporator 12. For example, the
amount of absorption of the gas by the activated carbon may
increase as the temperature at the outlet of the evaporator 12
decreases. Therefore, the pressure within the thermosensitive
cylinder 22 may vary with changes in the temperature at the outlet
of the evaporator 12. As a result, the opening degree of the
throttle valve 21 of the expansion valve 20 may be controlled in
response to the difference between the pressure of the gas within
the thermosensitive cylinder 22 and the pressure of the refrigerant
at the outlet of the evaporator 12.
[0045] Preferably, if the superheat condition of the refrigerant at
the outlet of the evaporator is too high during a low load
condition (i.e., the refrigerant is in a substantially gaseous
state during a low load operation), the degree of opening of the
throttle valve 21 may be increased in order to increase the flow
rate of the refrigerant into the evaporator. As a result, the
refrigerant is prevented from reaching an excessive superheat
condition. FIG. 3 shows a schematic graph showing the relationship
between the lift of the throttle valve 21 and the pressure
difference (.DELTA.P) between the pressure within the first tube 29
(or the pressure within the upper side of the diaphragm chamber 22)
and the pressure at the outlet of the evaporator 12 (or the
pressure within the lower side of the diaphragm chamber 22). In
FIG. 3, P0 is a predetermined value at which the valve 21 starts to
open. Because cross-charge type expansion valves are well known in
the art, further details concerning the construction of the
expansion valve 20 are not necessary.
[0046] A representative method for operating the air conditioner 1
will now be described with reference to FIGS. 1 to 5. An
explanatory graph showing the characteristics of a cross charge
type expansion valve is shown in FIG. 4. A Mollier chart for a
cooling medium circulation process of the air controlling circuit
is shown in FIG. 5.
[0047] Referring to FIG. 5, the relationship between pressure P and
enthalpy h for a phase change during the cooling medium circulation
process generally may be represented by the Mollier chart shown in
FIG. 5. In a phase change, as from a liquid to a gas, the change in
enthalpy of the system is the latent heat of vaporization. As the
air conditioner 1 is operated to drive the compressor C, saturated
refrigerant vapor A1' within the air conditioning circuit may be
drawn into and adiabatically compressed by the compressor C and
then may be discharged into the air conditioning circuit 2 as a
superheated refrigerant vapor A2' that has a relatively high
temperature and high pressure.
[0048] The superheated refrigerant vapor A2' discharged from the
compressor C may be isobarically cooled (Q (10)) and be liquefied
within the condenser 10 and the receiver 14 so as to become a
liquid cooling medium A3. That is, the vapor A2' is cooled without
changing pressure. The liquid cooling medium A3 may then be
expanded by the expansion valve 20 and the evaporator 12 in order
to generate a gas-liquid refrigerant vapor A4. The gas-liquid vapor
A4 may subsequently flow into the evaporator 12 and cool the air
passing across the evaporator 12 (which cooled air will be supplied
to the vehicle interior) through heat exchange between the
gas-liquid vapor A4 and the air. Hence, the gas-liquid vapor A4
absorbs energy from the air (Q (12)), which causes the liquid
content of the gas-liquid vapor A4 to isobarically vaporize. As a
result, the gas-liquid vapor A4 may become a substantially
saturated vapor A1', which is again suctioned into and pressurized
by the compressor C.
[0049] In this embodiment, the gas/liquid state of the cooling
medium at the outlet of the evaporator 12 may vary in response to
the degree of valve opening of the expansion valve 20. For example,
although the compressor C may compress the saturated refrigerant
vapor A1' into the superheated refrigerant vapor A2', the
compressor also may compress superheated refrigerant vapor AI into
superheated refrigerant vapor A2. That is, the degree of valve
opening of expansion valve 20 will determine the enthalpy h of the
refrigerant exhausted from the evaporator 12, and thus the state of
the refrigerant that is supplied to the compressor C. Because a
sufficient amount of lubrication oil must always be supplied to the
operating compressor C and liquid refrigerant conveys lubrication
oil more readily than gaseous lubrication oil, it is advantageous
to control the state of the refrigerant exhausted from evaporator
12 and drawn into compressor C in order to ensure that compressor C
is adequately lubricated.
[0050] By incorporating the cross-charge expansion valve 20 in the
representative embodiment, the superheat condition SH1 of the
cooling medium may vary in response to the temperature T(12) at the
outlet of the evaporator 12. In contrast, when a superheated (SH)
expansion valve is used instead of the expansion valve 20, the
superheat condition SH2 of the cooling medium may be a fixed value
irrespective of changes in the temperature T(12).
[0051] When the amount of energy Q(12) to be exchanged between the
cooling medium and the conditioning air becomes greater (i.e., the
air controlling load is increased) during the circulation of
cooling medium in the air controlling circuit 2, the relative
amount of vaporized cooling medium within the evaporator 12 may
increase. Therefore, the temperature T(12) at the outlet of the
evaporator 12 may increase. According to the representative
embodiment, the superheat condition SH1 of the cooling medium may
increase as the temperature T(12) increases. As a result, the
superheated cooling medium may return to the compressor C.
[0052] On the other hand, when the amount of energy Q(12) to be
exchanged between the cooling medium and the conditioning air
becomes less (i.e., the air controlling load is decreased) during
the circulation of cooling medium, the amount of heat that may be
absorbed by the conditioning air from the cooling medium flowing
through the evaporator 12 may decrease. Therefore, the temperature
T(12) at the outlet of the evaporator 12 may decrease. According to
the representative embodiment, the superheat condition SH1 of the
cooling medium may decrease as the temperature T(12) decreases. As
a result, the cooling medium at the outlet of the evaporator 12 may
not be completely vaporized (i.e., the cooling medium will be in a
dual gas-liquid state).
[0053] As discussed above, lubrication oil is disposed within the
cooling medium in order to reliably lubricate sliding parts within
the housing of the compressor C. Known compressors generally
utilize a lubrication oil recovering device for preventing the
lubrication oil from leaking out into the air conditioning circuit
along with the cooling medium that is discharged from the
compressor housing. For example, in an air conditioning circuit
incorporating a SH-type expansion valve, the cooling medium that
returns to the compressor is always in the state of a heated vapor.
However, when the flow rate of the cooling medium decreases during
a low load operation of the air conditioner, the lubrication oil
may not properly circulate with the relatively low flow of the
gaseous cooling medium. Thus, the compressor C may not be properly
lubricated.
[0054] According to the representative air conditioner 1, the
electrically powered compressor C does not require a lubrication
oil recovery device. Instead, the cross-type expansion valve 20 may
be incorporated to reliably circulate the lubrication oil during
all workloads on the compressor C. In other words, the cross-type
expansion valve 20 ensures that the cooling medium is always at a
proper condition (i.e., dual-phase or substantially gaseous) in
order to reliably supply lubrication oil to the moving parts within
the compressor C while also sufficiently cooling the air that will
be supplied to the vehicle interior. Thus, the expansion valve 20
may serve to vary the superheat condition of the cooling medium in
response to the operation load applied to the air conditioner 1. In
particular, when the air conditioner 1 operates under a relatively
low load, in which the lubrication oil may not smoothly circulate,
the expansion valve 20 may serve to provide a partially liquefied
refrigerant vapor (i.e., a dual phase gas-liquid) at the outlet of
the expansion valve. Thus, a dual phase refrigerant may be returned
to the compressor C.
[0055] Therefore, the lubrication oil may reliably return to the
compressor C along with the flow of the liquefied cooling medium.
As a result, the circulation properties of the lubrication oil may
be improved with respect to known air conditioners incorporating
SH-type expansion valves, in particular during a low load operation
of the air conditioner 1. Although the temperature of the cooling
medium at the outlet of the expansion valve 20 may increase during
the high load operation, this may not cause any problem, because
the lubrication oil may flow along with the gaseous cooling medium
that flows at a higher rate. Consequently, the circulation
properties of the lubrication oil in the air conditioning circuit 2
may be improved.
[0056] According to the representative embodiment, when the air
conditioner is operated under low load and the flow rate of
circulation of the cooling medium is relatively small, the
cross-charge expansion valve 20 may decrease the degree of
superheat of the cooling medium that returns to the compressor C.
In that case, the cooling medium may be brought into a saturated
state or a partly liquefied state, which state may improve the
circulating properties of the cooling medium and the lubrication
oil. Therefore, air conditioners having improved circulating
properties can be easily attained at a lower cost by incorporating
the representative expansion valve 20 in place of a known
lubrication oil recovery device.
[0057] The present teachings should not be limited to the
representative embodiment, but instead, may be used for different
applications and may be modified in various ways. For example, the
cross-charge type expansion valve 20 may be replaced with another
device or devices that are capable of causing the superheat
condition of the cooling medium that returns to the compressor C to
appropriately change in order to supply adequate lubrication oil to
the compressor. For example, expansion valves of different types or
control valves can be advantageously utilized to vary the
cross-sectional area of the flow line in the air conditioning
circuit to control the refrigerant temperature.
* * * * *