U.S. patent application number 09/795542 was filed with the patent office on 2001-09-06 for air conditioning system with compressor protection.
Invention is credited to Honda, Keita.
Application Number | 20010018831 09/795542 |
Document ID | / |
Family ID | 18580772 |
Filed Date | 2001-09-06 |
United States Patent
Application |
20010018831 |
Kind Code |
A1 |
Honda, Keita |
September 6, 2001 |
Air conditioning system with compressor protection
Abstract
An air conditioning system includes compressor protective means
for protecting a compressor. The compressor protective means
includes first and second protective values. The first protective
value is set for preventing a failure of a compressor. The second
protective value is lower than the first protective value in order
to prevent a high pressure in a refrigerant cycle system from
reaching the first protective value. The compressor protective
means sets the second protective value such that the second
protective value used before an elapse of a predetermined time
period from startup of the compressor is lower than the second
protective value used after the elapse of the predetermined time
period.
Inventors: |
Honda, Keita; (Okazaki-city,
JP) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, PLC
P.O. BOX 828
BLOOMFIELD HILLS
MI
48303
US
|
Family ID: |
18580772 |
Appl. No.: |
09/795542 |
Filed: |
February 28, 2001 |
Current U.S.
Class: |
62/228.1 ;
165/281; 165/63; 62/228.3 |
Current CPC
Class: |
F25B 2600/021 20130101;
F25B 49/022 20130101; B60H 1/3225 20130101; F25B 2500/07
20130101 |
Class at
Publication: |
62/228.1 ;
62/228.3; 165/281; 165/63 |
International
Class: |
F25B 029/00; F25B
001/00; F25B 049/00; G05D 015/00; G05D 016/00; G05D 023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 6, 2000 |
JP |
2000-60459 |
Claims
What is claimed is:
1. An air conditioning system comprising: a refrigerant cycle
including a compressor compressing refrigerant, a condenser
condensing refrigerant, a decompressing unit decompressing
refrigerant, an evaporator evaporating refrigerant, and an
accumulator disposed between said evaporator and said compressor to
separate refrigerant into gas refrigerant and liquid refrigerant,
wherein said compressor, said condenser, said evaporator and said
accumulator are connected to circulate refrigerant in said
refrigerant cycle; target capacity setting means for setting a
target capacity of said compressor; compressor control means for
controlling a capacity of said compressor based on said target
capacity set by said target capacity setting means; and compressor
protective means having first and second protective values, said
first protective value being set for preventing a failure of said
compressor, said second protective value being lower than said
first protective value in order to prevent a high pressure in said
refrigerant cycle system from reaching said first protective value,
said compressor protective means maintaining or reducing said
capacity of said compressor when said high pressure exceeds said
second protective value, said compressor protective means turning
off said compressor when said high pressure exceeds said first
protective value, wherein said compressor protective means sets
said second protective value in such a manner that said second
protective value used before an elapse of a predetermined time
period from startup of said compressor is lower than said second
protective value used after said elapse of said predetermined time
period.
2. An air conditioning system according to claim 1, wherein: said
second protective value includes at least a high-pressure side
second protective value; said compressor protective means reduces
said capacity of said compressor when said high pressure exceeds
said high-pressure side second protective value; and said
compressor protective means sets said high-pressure side second
protective value in such a manner that said high-pressure side
second protective value used before said elapse of said
predetermined time period from said startup of said compressor is
lower than said high-pressure side second protective value used
after said elapse of said predetermined time period.
3. An air conditioning system according to claim 1, wherein: said
second protective value includes at least a low-pressure side
second protective value; said compressor protective means maintains
said capacity of said compressor when said high pressure exceeds
said low-pressure side second protective value; and said compressor
protective means sets said low-pressure side second protective
value in such a manner that said low-pressure side second
protective value used before said elapse of said predetermined time
period from said startup of said compressor is lower than said
low-pressure side second protective value used after said elapse of
said predetermined time period.
4. An air conditioning system according to claim 1, wherein: said
second protective value includes a high-pressure side second
protective value and a low-pressure side second protective value
that is lower than said high-pressure side second protective value;
said compressor protective means maintains said capacity of said
compressor when said high pressure exceeds said low-pressure side
second protective value; said compressor protective means reduces
said capacity of said compressor when said high pressure exceeds
said high-pressure side second protective value; said compressor
protective means sets said low-pressure side second protective
value in such a manner that said low-pressure side second
protective value used before said elapse of said predetermined time
period from said startup of said compressor is lower than said
low-pressure side second protective value used after said elapse of
said predetermined time period.
5. An air conditioning system according to claim 1, wherein said
compressor is driven by an electrical motor.
6. An air conditioning system according to claim 1, wherein said
capacity of said compressor is a rotational speed of said
compressor.
7. An air conditioning system according to claim 1, wherein said
second protective value is reduced during a cooling mode of said
air conditioning system.
8. An air conditioning system comprising: a refrigerant cycle
system including a compressor compressing refrigerant; a condenser
condensing refrigerant; a decompressing unit decompressing
refrigerant; an evaporator evaporating refrigerant; and an
accumulator arranged between said evaporator and said compressor to
separate refrigerant into gas refrigerant and liquid refrigerant,
wherein said compressor, said condenser, said evaporator and said
accumulator are connected to circulate refrigerant in said
refrigerant cycle; target capacity setting means for setting a
target capacity of said compressor; compressor control means for
controlling a capacity of said compressor based on said target
capacity set by said target capacity setting means; and compressor
protective means having first and second protective values, said
first protective value being set for preventing a failure of said
compressor, said second protective value being lower than said
first protective value in order to prevent a high pressure in said
refrigerant cycle system from reaching said first protective value,
said second protective value including a high-pressure side second
protective value and a low-pressure side second protective value
that is lower than said high-pressure side second protective value,
said compressor protective means maintaining said capacity of said
compressor when said high pressure in said refrigerant cycle system
exceeds said low-pressure side second protective value, said
compressor protective means reducing said capacity of said
compressor when said high pressure exceeds said high-pressure side
second protective value, said compressor protective means turning
off said compressor when said high pressure exceeds said first
protective value; wherein said compressor protective means sets a
difference between said high-pressure side second protective value
and said low-pressure side second protective value in such a manner
that said difference before elapse of a predetermined time period
from startup of said compressor is smaller than said difference
after said elapse of said predetermined time period.
9. An air conditioning system according to claim 1, wherein said
decompressing unit is a fixed throttle.
10. An air conditioning system according to claim 8, wherein said
compressor is driven by an electrical motor.
11. An air conditioning system according to claim 8, wherein said
capacity of said compressor is a rotational speed of said
compressor.
12. An air conditioning system according to claim 8, wherein said
second protective value is reduced during a cooling mode of said
air conditioning system.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on and incorporates herein by
reference Japanese Patent Application No. 2000-60459 filed on Mar.
6, 2000.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an air conditioning system
that carries out a protective control operation of a compressor
when a high pressure in a refrigerant cycle of the air conditioning
system becomes abnormally high, to prevent a failure of the
compressor.
[0004] 2. Description of Related Art
[0005] In a known type of refrigerant cycle system having an
accumulator, if a compressor is operated while a high pressure in
the refrigerant cycle system is abnormally high, the compressor
will fail. To prevent the failure of the compressor, a first
protective value is set near an upper tolerable pressure limit of
the compressor. When the high pressure of the refrigerant cycle
system exceeds the first protective value, the compressor is
forcefully turned off.
[0006] Furthermore, a second protective value that is lower than
the first protective value is set to prevent the high pressure from
reaching the first protective pressure. When the high pressure
exceeds the second protective value, a current rotational speed
(capacity) of the compressor is maintained or reduced.
Specifically, the second protective value is split into a
low-pressure side second protective value and a high-pressure side
second protective value. When the high pressure in the refrigerant
cycle system exceeds the low-pressure side second protective value,
the current compressor rotational speed is maintained. When the
high pressure exceeds the high-pressure side second protective
value, the compressor rotational speed is reduced. However, in the
refrigerant cycle system, each one of the protective values is
always the same regardless of operation time of the compressor.
This causes the following problem at startup of the compressor.
[0007] That is, at the startup of the compressor, the compressor
rotational speed increases very rapidly from zero to a target
rotational speed, and thereby the high pressure in the refrigerant
cycle system also increases very rapidly.
[0008] Also, at the startup of the compressor, gaseous refrigerant
remained in a condenser near an outlet of the condenser is
discharged from the outlet of the condenser without completely
dissipating its heat. Thus, a gas to liquid ratio of refrigerant at
the outlet of the condenser increases. In the refrigerant cycle
system having the accumulator, a gas-liquid separator (receiver)
that separates refrigerant into gas refrigerant and liquid
refrigerant is not arranged between the condenser and a
decompressor. As a result, refrigerant discharged from the outlet
of the condenser is not separated into the gas refrigerant and the
liquid refrigerant before entering into the decompressor. Thus,
when the gas to liquid ratio of refrigerant is increased at the
outlet of the condenser, a throttle degree of the decompressor
increases, and thereby a high-pressure side refrigerant pressure of
the refrigerant cycle system rapidly increases.
[0009] As a result, as shown in FIG. 10, the high pressure exceeds
the second protective values (HPV2, LPV2) at the startup of the
compressor. In FIG. 10, PV1 indicates the first protective value,
HPV2 indicates the high-pressure side second protective value, and
LPV2 indicates the low-pressure side second protective value.
[0010] When the high pressure exceeds the second protective values,
the current compressor rotational speed is maintained or reduced.
However, due to the rapid increase of the high pressure, the high
pressure may also exceed the first protective value (PV1), causing
forceful shutdown of the compressor. If this happens, the
compressor needs to be restarted, and the restart of the compressor
disadvantageously requires a certain amount of time.
[0011] Furthermore, when the high pressure exceeds the low-pressure
side second protective value (LPV2) and then the high-pressure side
second protective value (LPV2), the compressor rotational speed is
forcefully reduced. In this way, the high pressure decreases below
the high-pressure side second protective value (HPV2). At this time
point, the current compressor rotational speed is maintained to
keep the high pressure between the high-pressure side second
protective value (HPV2) and the low-pressure side second protective
value (LPV2). However, the compressor rotational speed decreases at
a maximum rate. Thus, the high pressure may continue to decrease
and thereby may become lower than the low-pressure side second
protective value (LPV2). In such a case, since the current
operating condition of the air conditioning system has not been
changed and thereby still causes the high pressure to increase.
Thus, the high pressure may increase once again, and start
performance of the compressor is deteriorated.
SUMMARY OF THE INVENTION
[0012] The present invention addresses the above-described
problems. Thus, it is an objective of the present invention to
provide an air conditioning system having a refrigerant cycle
system, which improves starting performance of a compressor while
protecting the compressor.
[0013] To achieve the objective of the present invention, an air
conditioning system has a compressor protective control unit having
first and second protective values. The first protective value is
set for preventing a failure of a compressor. The second protective
value is lower than the first protective value in order to prevent
a high pressure in a refrigerant cycle system from reaching the
first protective value. The compressor protective control unit
maintains or reduces a capacity of the compressor when the high
pressure in the refrigerant cycle system exceeds the second
protective value. The compressor protective control unit turns off
the compressor when the high pressure exceeds the first protective
value. The compressor protective control unit sets the second
protective value such that the second protective value used before
an elapse of a predetermined time period from startup of the
compressor is lower than the second protective value used after the
elapse of the predetermined time period. Accordingly, the air
conditioning system improves start performance of the compressor,
while protecting the compressor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Additional objects and advantages of the present invention
will be more readily apparent from the following detailed
description of a preferred embodiment when taken together with the
accompanying drawings, in which:
[0015] FIG. 1 is a schematic diagram of an air conditioning system
of an electric vehicle according to a preferred embodiment of the
present invention;
[0016] FIG. 2 is a block diagram showing a control unit of the air
conditioning system according to the embodiment;
[0017] FIG. 3 is a flow diagram showing a control operation carried
out by a microcomputer of the air conditioning system;
[0018] FIG. 4 is a graph for setting an operation mode among a
cooling mode, a blowing mode and a heating mode according to the
first embodiment;
[0019] FIG. 5A is a view showing a membership function used during
the cooling mode, and
[0020] FIG. 5B is a view showing an another membership function
used during the cooling mode;
[0021] FIG. 6 is a view showing a fuzzy rule used during the
cooling mode;
[0022] FIG. 7A is a view showing a membership function used during
the heating mode, and
[0023] FIG. 7B is a view showing an another membership function
used during the heating mode;
[0024] FIG. 8 is a view showing a fuzzy rule used during the
heating mode;
[0025] FIG. 9 is a flow diagram showing a protective control
operation of a compressor according to the embodiment; and
[0026] FIG. 10 is a graph showing characteristics of a high
pressure, a target rotational speed and a rotational speed of a
compressor at a start operation.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENT
[0027] An air conditioning system of an electric vehicle according
to a preferred embodiment of the present invention will be
described with reference to FIGS. 1-9. First, constructions of an
interior air conditioning unit 1 placed in an interior of a
passenger compartment and a refrigerant cycle system 9 will be
described with reference to FIG. 1.
[0028] As shown in FIG. 1, the interior air conditioning unit 1
includes an air conditioning case 2. The air conditioning case 2
defines an air passage that leads conditioned air into the interior
of the passenger compartment. At upstream of the air conditioning
case 2, an inside air suction port 3, an outside air suction port 4
and an inside/outside air switching door 5 are arranged. The inside
air suction port 3 is provided for sucking inside air from the
passenger compartment. The outside air suction port 4 is provided
for sucking outside air outside the passenger compartment. The
inside/outside air switching door 5 is disposed for selectively
opening and closing the inside air suction port 3 and the outside
air suction port 4. The inside/outside air switching door 5 is
driven by a servo motor 6 (see FIG. 2).
[0029] A fan 7 for generating an air flow in the air passage is
disposed downstream of the inside/outside air switching door 5. The
fan 7 is driven by a blower motor 8. An interior evaporator 10
constituting a part of the refrigerant cycle system 9 is disposed
downstream of the fan 7. The interior evaporator 10 is used for
cooling air by a heat absorbing reaction of refrigerant flowing
through the interior evaporator 10 during a cooling mode which will
be described in detail below.
[0030] An interior condenser 11 constituting a part of the
refrigerant cycle system 9 is located downstream of the interior
evaporator 10. The interior condenser 11 is used for heating air by
heat radiating reaction of refrigerant flowing through the interior
condenser 11 during a heating mode which will be described in
detail below.
[0031] An air mixing door 12 is located adjacent to the interior
condenser 11. The air mixing door 12 adjusts the amount of air
passing through the interior condenser 11 and the amount of air
bypassing the interior condenser 11. The air mixing door 12 is
driven by a servo motor 13 (see FIG. 2).
[0032] At a downstream side of the air conditioning case 2, a face
air outlet, a foot air outlet and a defroster air outlet are
provided. The face air outlet is provided for blowing conditioned
air toward the upper half body of a passenger in the passenger
compartment. The foot air outlet is provided for blowing
conditioned air toward the feet of the passenger in the passenger
compartment. The defroster air outlet is provided for blowing
conditioned air toward an inner surface of a windshield. An air
outlet mode switching member is provided for opening and closing
the face air outlet, the foot air outlet and the defroster air
outlet.
[0033] The refrigerant cycle system 9 is a heat pump type
refrigerant cycle system that cools and heats the passenger
compartment by use of the interior evaporator 10 and the interior
condenser 11, respectively. Besides the evaporator 10 and the
condenser 11, the refrigerant cycle system 9 further includes a
compressor 14, an exterior heat exchanger 15, a heating capillary
tube 16, a cooling capillary tube 17, an accumulator 18 and
solenoid valves 19-21, all of which are fluidly connected by a
refrigerant pipe 22.
[0034] Exterior fans 23 for blowing air toward the exterior heat
exchanger 15 are arranged adjacent to the exterior heat exchanger
15. The exterior fans 23 are driven by an exterior fan motor 24
(FIG. 2).
[0035] The compressor 14 sucks, compresses and then discharges
refrigerant when it is driven by an electric motor 25 (FIG. 2). The
electric motor 25 and the compressor 14 are integrally arranged
within a sealed case. A rotational speed of the electric motor 25
is controlled by an inverter 26 (FIG. 2) to be linearly changed.
Energization of the inverter 26 is controlled by a control device
27 (FIG. 2).
[0036] The exterior heat exchanger 15 acts as an evaporator during
a heating mode and acts as a condenser during a cooling mode.
[0037] The heating capillary tube 16 acts as decompressing means
during the heating mode. The cooling capillary tube 17 acts as
decompressing means during the cooling mode. Each capillary tube 16
or 17 acts as a fixed throttle for restricting a flow of
refrigerant. Therefore, refrigerant decompresses while passing
through the heating capillary tube 16 or the cooling capillary tube
17.
[0038] The accumulator 18 is arranged in the refrigerant cycle
system 9 between the compressor 14 and the interior evaporator 10
or the exterior heat exchanger 15. The accumulator 18 is a
gas-liquid separator for separating refrigerant from the interior
evaporator 10 or the exterior heat exchanger 15 into gas
refrigerant and liquid refrigerant. Because of the accumulator 18,
the compressor 14 can always suck the gaseous refrigerant.
[0039] Energization of each one of the solenoid valves 19-21 is
controlled by the control device 27 (FIG. 2).
[0040] The control device 27 of the vehicle air conditioning system
according to the present embodiment will be described with
reference to FIG. 2.
[0041] The control device 27 includes a known microcomputer, an A/D
converter circuit, a timer and the like. The microcomputer includes
a CPU, a ROM, a RAM and the like.
[0042] The control device 27 is activated when a key switch (not
shown) is turned on and power from a battery (not shown) is
supplied to the control device 27. The key switch is turned on or
off when the vehicle passenger turns a key cylinder (not shown)
with a key in a corresponding direction.
[0043] With reference to FIG. 2, an inside air temperature sensor
28 measures an inside air temperature of the passenger compartment.
An outside air temperature sensor 29 measures an outside air
temperature of the passenger compartment. A solar radiation sensor
30 measures the amount of solar radiation reaching the interior of
the passenger compartment. An exterior refrigerant sensor 31
measures a temperature of refrigerant at an outlet of the exterior
heat exchanger 15. A post-evaporator sensor 32 measures a
temperature (hereinafter called "post-evaporator temperature") of
air right after passing through the interior evaporator 10. A
pressure sensor 33 measures a pressure (hereinafter called "high
pressure) of refrigerant at the high pressure side of the
refrigerant cycle system 9. Signals outputted from these sensors
28-33 are fed to input terminals of the control device 27.
Furthermore, signals outputted from an air conditioning setting
member (such as a temperature setting unit) provided on a control
panel 34 are also fed to the input terminals of the control device
27.
[0044] The signals outputted from the sensors 28-33 and the signals
outputted from the control panel 34 are converted from analog to
digital by the A/D converter circuit before entering the
microcomputer.
[0045] Control signals are outputted from output terminals of the
control device 27 to the blower motor 8, the servo motors 6 and 13,
the solenoid valves 19-21, the exterior fan motor 24 and the
inverter 26.
[0046] A control process that is carried out by the microcomputer
when the key switch is turned on will be discussed with reference
to a flow diagram shown in FIG. 3.
[0047] When a control routine shown in FIG. 3 starts, an
initialization is performed at step 100. Then, at step 110, the
signals from the sensors 28-33 and the signals from the control
panel 34 are read. Next, at step 120, a target air temperature TAO
that is a target temperature of air blown into the passenger
compartment from the air conditioning system is computed according
to the following equation (1) stored in the ROM:
TAO(.degree.
C.)=Kset.times.Tset-Kr.times.Tr-Kam.times.Tam-Ks.times.Ts+C (1)
[0048] where:
[0049] Tset is a set air temperature of the passenger compartment
set by the vehicle passenger through the temperature setting unit
provided on the control panel 34;
[0050] Tr is the inside air temperature measured by the inside air
temperature sensor 28;
[0051] Tam is the outside air temperature measured by the outside
air temperature sensor 29;
[0052] Ts is the amount of solar radiation measured by the solar
radiation sensor 30;
[0053] Kset, Kr, Kam and Ks are gains; and
[0054] C is a constant.
[0055] Then, at step 130, an air suction mode is selected between
the inside air mode and the outside air mode based on the target
air temperature TAO using a control characteristic (not shown).
Then, control moves to step 140 where a blower voltage applied to
the blower motor 8 is controlled based on the TAO using a control
characteristic (not shown).
[0056] At step 150, an operation mode is selected among the cooling
mode, the blowing mode and the heating mode based on a difference
between the TAO and a sucked air temperature T.sub.in, as shown in
FIG. 4. The sucked air temperature T.sub.in is the inside air
temperature Tr (T.sub.in=Tr) during the inside air mode, and is the
outside air temperature T.sub.am (T.sub.in=T.sub.am) during the
outside air mode.
[0057] During the cooling mode, the exterior fans 23 are operated.
Furthermore, in the refrigerant cycle system 9, the solenoid valve
19 is opened, and the solenoid valves 20 and 21 are closed. In this
way, refrigerant in the refrigerant cycle system 9 is circulated
through the compressor 14, the interior condenser 11, the exterior
heat exchanger 15, the cooling capillary tube 17, the interior
evaporator 10, the accumulator 18 and the compressor 14 in this
order. In addition, in the interior air conditioning unit 1, the
air mixing door 12 is positioned to completely close off an inlet
opening of the interior condenser 11 so that all air bypasses the
interior condenser 11.
[0058] During the blowing mode, both the compressor 14 and the
exterior fans 23 are turned off.
[0059] During the heating mode, the exterior fans 23 are operated.
Furthermore, in the refrigerant cycle system 9, the solenoid valves
19 and 21 are closed, and the solenoid valve 20 is opened. In this
way, refrigerant in the refrigerant cycle system 9 is circulated
through the compressor 14, the interior condenser 11, the heating
capillary tube 16, the exterior heat exchanger 15, the accumulator
18 and the compressor 14 in this order. In addition, in the
interior air conditioning unit 1, the air mixing door 12 is
positioned to fully open the inlet opening of the interior
condenser 11 so that all air passes through the interior condenser
11.
[0060] At the following step 160, the rotational speed (i.e.,
rotation number) of the compressor 14 is controlled as follows for
each of the cooling mode and the heating mode. During the blowing
mode, the control operation of step 160 is not performed.
[0061] (Cooling Mode)
[0062] First, a deviation E.sub.n between the target air
temperature TAO and the post-evaporator temperature TE measured by
the post-evaporator temperature sensor 32, is computed according to
the following equation (2).
E.sub.n=TAO-TE (2)
[0063] Then, a change rate E.sub.dot of the deviation E.sub.n is
computed according to the following equation (3).
E.sub.dot=E.sub.n-E.sub.n-1 (3)
[0064] In this embodiment, E.sub.n is renewed every four seconds,
so that E.sub.n-1 is a previous value obtained four seconds before
E.sub.n.
[0065] Then, a change rate .DELTA.f of the compressor rotational
speed which increases or decreases relative to the previous
rotational speed f.sub.n-1 of the compressor 14 measured four
seconds before, is computed. The change rate .DELTA.f of the
compressor rotational speed is computed through a fuzzy logic based
on membership functions shown in FIGS. 5A and 5B and also based on
rule values shown in FIG. 6 using the above computed E.sub.n and
E.sub.dot. The membership functions and the rule table are stored
in the ROM. Specifically, based on CF1 obtained from FIG. 5A and
CF2 obtained from FIG. 5B, a goodness of fit CF is computed
according to the following equation (4).
CF=CF1.times.CF2 (4)
[0066] Then, based on the computed goodness of fit CF and a rule
value obtained from FIG. 6, the change rate .DELTA.f of the
compressor rotational speed is computed according to the following
equation (5).
.DELTA.f=.SIGMA.(CF.times.rule value)/.SIGMA.CF (rpm/4 sec) (5)
[0067] A next compressor rotational speed f.sub.n is computed
according to the following equation (6).
f.sub.n=f.sub.n-1+.DELTA.f (rpm/4 sec) (6)
[0068] Then, the energization of the inverter 26 is controlled in
such a way that an actual compressor rotational speed becomes the
computed next compressor rotational speed f.sub.n.
[0069] (Heating Mode)
[0070] During the heating mode, a target pressure (hereinafter
called "target high pressure") SPO of refrigerant in the high
pressure side of the refrigerant cycle system 9 is determined based
on the target air temperature TAO. Then, a deviation E.sub.n
between the target high pressure SPO and the high pressure SP
measured by the pressure sensor 33 is computed according to the
following equation (7).
E.sub.n=SPO-SP (7)
[0071] Then, a rate of change .DELTA.f of the compressor rotational
speed, which increases or decreases relative to the previous
compressor rotational speed f.sub.n-1 measured four seconds before,
is computed. The change rate .DELTA.f of the compressor rotational
speed is computed through a fuzzy logic based on membership
functions shown in FIGS. 7A and 7B and also based on a rule table
shown in FIG. 8 using the above computed E.sub.n and E.sub.dot. The
membership functions and the rule table are stored in the ROM.
Specifically, based on CF1 obtained from FIG. 7A and CF2 obtained
from FIG. 7B, a goodness of fit CF is computed according to the
above equation (4). Then, based on the computed goodness of fit CF
and a rule value obtained from the rule table shown in FIG. 8, the
change rate .DELTA.f of the compressor rotational speed is computed
according to the above equation (5).
[0072] Thereafter, a next compressor rotational speed f.sub.n is
computed according to the above equation (6). Then, the
energization of the inverter 26 is controlled in such a way that an
actual compressor rotational speed becomes the computed next
compressor rotational speed f.sub.n.
[0073] In the above-described control operation of the compressor
rotational speed, when the high pressure SP becomes abnormally
high, a torque applied on an output shaft (not shown) of the
electric motor 25 becomes high, thereby causing overheating and
braking of a winding (not shown) of the electric motor 25. In the
present embodiment, a control operation (hereinafter called "a
protective control operation of the compressor 14") for preventing
an occurrence of such an incidence is carried out.
[0074] The protective control operation of the compressor 14 is a
main feature of the present embodiment and thereby is described in
detail with reference to FIG. 9. Similar to the routine shown in
FIG. 3, a routine shown in FIG. 9 starts when the key switch is
turned on.
[0075] When the routine shown in FIG. 9 starts, control routine
moves to step 200 where it is determined whether the current
operation mode is the cooling mode. When the operation mode is the
cooling mode, control routine moves to step 210. When the operation
mode is not the cooling mode, control routine moves to step
220.
[0076] At step 210, it is determined whether a predetermined time
period (2 minutes, for example) has elapsed from time of switching
on of the key switch, i.e., from time of startup of the compressor
14. In this embodiment, the predetermined time period is the time
period required for refrigerant at the outlet of the exterior heat
exchanger 15 to be completely turned into liquid refrigerant from
the time of startup of the compressor 14 during the cooling
mode.
[0077] If the determination at step 210 is "YES", control routine
proceeds to step 220. If the determination at step 210 is "NO",
control routine proceeds to step 230.
[0078] Protective values for limiting the high pressure SP during a
normal operating period are set at step 220. That is, a first
protective value SP.sub.a is set to 27.5 kg/cm.sup.2G. A
high-pressure side second protective value SP.sub.b is set to 24
kg/cm.sup.2G. A low-pressure side second protective value SP.sub.c
is set to 22 kg/cm.sup.2G.
[0079] The first protective value SP.sub.a is set around an upper
tolerable pressure limit of the compressor 14 to prevent a failure
of the compressor 14 (electric motor 25), that may be caused when
the compressor 14 is operated while the high pressure of the
refrigerant cycle system 9 is abnormally high.
[0080] The second protective values SP.sub.b and SP.sub.c are set
below the first protective value SP.sub.a in order to prevent the
high pressure SP from reaching the first protective value SP.sub.a.
The low-pressure side second protective value SP.sub.c is lower
than the high-pressure side second protective value SP.sub.b.
[0081] At step 230, protective values for limiting the high
pressure SP during the startup period of the compressor 14 are set.
That is, a first protective value SP.sub.a is set to 27.5
kg/cm.sup.2G. The high-pressure side second protective value
SP.sub.b is set to 23 kg/cm.sup.2G. The low-pressure side second
protective value SP.sub.c is set to 19 kg/cm.sup.2G.
[0082] In other words, the second protective values SP.sub.b and
SP.sub.c before elapse of the predetermined time period are set
lower than the second protective values SP.sub.b and SP.sub.c after
the elapse of the predetermined time period, respectively.
Furthermore, a difference between the high-pressure side second
protective value SP.sub.b and the low-pressure side second
protective value SP.sub.c before the elapse of the predetermined
time period is set greater than a difference between the
high-pressure side second protective value SP.sub.b and the
low-pressure side second protective value SP.sub.c after the elapse
of the predetermined time period.
[0083] At the next step 240, it is determined whether the high
pressure SP is higher than the first protective value SPa. If the
determination at step 240 is "YES", control routine moves to step
250 where the compressor 14 is forcefully turned off. If the
determination at step 240 is "NO", control routine moves to step
260.
[0084] At step 260, it is determined whether the high pressure SP
is higher than the high-pressure side second protective value
SP.sub.b. If the determination at step 260 is "YES", control
routine moves to step 270. At step 270, the change rate .DELTA.f of
the compressor rotational speed is set to -600 rpm/4 sec to
forcefully reduce the compressor rotational speed f.sub.n. If the
determination at step 260 is "NO", control moves to step 280. In
this embodiment, as is obvious from the rule table shown in FIG. 6,
-600 rpm/4 sec is the change rate .DELTA.f of the compressor
rotational speed required for achieving a maximum degree of
reduction in the compressor rotational speed f.sub.n.
[0085] At step 280, it is determined whether the high pressure SP
is higher than the low-pressure side second protective value
SP.sub.c. If the determination at step 280 is "YES", control
routine moves to step 290 where the change rate .DELTA.f of the
compressor rotational speed is set to zero, thereby forcefully
maintaining the current compressor rotational speed f.sub.n.
[0086] According to the above-described embodiment, the second
protective values SP.sub.b and SP.sub.c before the elapse of the
predetermined time period are lower than the second protective
values SP.sub.b and SP.sub.c after the elapse of the predetermined
time period, respectively.
[0087] In this way, even if the high pressure SP rises quickly at
the startup of the compressor 14, the compressor rotational speed
f.sub.n is forcefully reduced and maintained at the early stage, so
that the high pressure SP is effectively prevented from exceeding
the first protective value SP.sub.a, thereby preventing the
forceful stop of the compressor 14.
[0088] The difference between the high-pressure side second
protective value SP.sub.b and the low-pressure side second
protective value SP.sub.c before the elapse of the predetermined
time period is increased in comparison to the difference between
the high-pressure side second protective value SP.sub.b and the
low-pressure side second protective value SP.sub.c after the elapse
of the predetermined time period. Thus, the time period provided
for maintaining the rotational speed f.sub.n is lengthened,
allowing prevention of problematic hunting of the high pressure SP
at the startup of the compressor 14.
[0089] Although the present invention has been fully described in
connection with the preferred embodiment thereof with reference to
the accompanying drawings, it is to be noted that various changes
and modifications will become apparent to those skilled in the
art.
[0090] For example, in the above embodiment, the high-pressure side
second protective value SP.sub.b and the low-pressure side second
protective value SP.sub.c are provided as the second protective
value. Furthermore, both the high-pressure side second protective
value SP.sub.b and the low-pressure side second protective value
SP.sub.c before the elapse of the predetermined time period are set
below the high-pressure side second protective value SP.sub.b and
the low-pressure side second protective value SP.sub.c after the
elapse of the predetermined time period, respectively.
Alternatively, only one of the high-pressure side second protective
value SP.sub.b and the low-pressure side second protective value
SP.sub.c before the elapse of the predetermined time period can be
set below the corresponding one of the high-pressure side second
protective value SP.sub.b and the low-pressure side second
protective value SP.sub.c after the elapse of the predetermined
time period.
[0091] Furthermore, instead of providing both the high-pressure
side second protective value SP.sub.b and the low-pressure side
second protective value SP.sub.c as the second protective value, it
is possible to use only one of the high-pressure side second
protective value SP.sub.b and the low-pressure side second
protective value SP.sub.c.
[0092] In the above-described embodiment, the difference between
the high-pressure side second protective value SP.sub.b and the
low-pressure side second protective value SP.sub.c before the
elapse of the predetermined time period is made greater than the
difference between the high-pressure side second protective value
SP.sub.b and the low-pressure side second protective value SP.sub.c
after the elapse of the predetermined time period. This can be
accomplished without lowering the low-pressure side second
protective value SP.sub.c by setting the high-pressure side second
protective value SP.sub.b before the elapse of the predetermined
time period to be higher than the high-pressure side second
protective value SP.sub.b after the elapse of the predetermined
time period.
[0093] In the above-described embodiment, whether the high pressure
SP exceeds each one of the protective values SP.sub.a, SP.sub.b and
SP.sub.c is determined by measuring the high pressure SP with the
pressure sensor 33 and comparing the measured high pressure SP with
each one of the protective values SP.sub.a, SP.sub.b and SP.sub.c.
However, the high pressure SP can be estimated based on, for
example, an output electric current of the inverter 26.
[0094] In the above-described embodiment, "the predetermined time
period" is the time period required for refrigerant discharged from
the outlet of the exterior heat exchanger 15 to be completely
turned into liquid refrigerant after the startup of the compressor
14 during the cooling mode. However, "the predetermined time
period" can be made longer than this time period.
[0095] In the above-described embodiment, the capillary tubes 16
and 17 are used as the decompressing means. The decompressing means
can be, for example, any other type of a fixed throttle, such as a
CTD, or can be any type of variable throttle, such as an
electromagnetic expansion valve.
[0096] In the above-described embodiment, the target rotational
speed f.sub.n of the compressor 14 is automatically determined
based on a thermal load of the vehicle interior at step 160.
Alternatively, the target rotational speed f.sub.n can be
determined based on the set air temperature of the passenger
compartment, that is set through the temperature setting unit.
[0097] Furthermore, in the above-described embodiment, when the
high pressure SP exceeds each one of the protective values
SP.sub.a, SP.sub.b and SP.sub.c, the protective control operation
is carried out by changing the rotational speed of the compressor
14. Instead of changing the rotational speed of the compressor 14,
a displacement of the compressor can be changed.
[0098] In the above-described embodiment, during the predetermined
time period after the startup of the compressor 14, the second
protective values SP.sub.b and SP.sub.c are set to be lowered, and
the difference between the high-pressure side second protective
value SP.sub.b and the low-pressure side second protective value
SP.sub.c is made larger. Although this operation is only conducted
during the cooling mode in the above-described embodiment, this
operation can be also conducted during the heating mode.
[0099] In the above-described embodiment, the temperature of air
blown out from the air conditioning system is controlled through
the fuzzy logic. This temperature can be controlled through any
other means.
[0100] In the above-described embodiment, the present invention is
typically applied to the air conditioning system of the electric
vehicle. The present invention is not limited to this and can be
applied to an air conditioning system of an engine vehicle or a
hybrid vehicle or an air conditioning system of a home or a
building.
[0101] Such changes and modifications are to be understood as being
within the scope of the present invention as defined by the
appended claims.
* * * * *