U.S. patent application number 11/805469 was filed with the patent office on 2008-11-27 for control method for a variable displacement refrigerant compressor in a high-efficiency ac system.
Invention is credited to Prasad S. Kadle, Mark J. Zima.
Application Number | 20080289347 11/805469 |
Document ID | / |
Family ID | 39708721 |
Filed Date | 2008-11-27 |
United States Patent
Application |
20080289347 |
Kind Code |
A1 |
Kadle; Prasad S. ; et
al. |
November 27, 2008 |
Control method for a variable displacement refrigerant compressor
in a high-efficiency AC system
Abstract
A high efficiency air conditioning system includes a
pneumatically-controlled variable displacement compressor and a
compressor clutch that is selectively cycled on and off to minimize
series re-heating of conditioned air. Conditioned air is discharged
after passing through an evaporator core, and a target value for
the evaporator outlet air temperature is determined based on the
desired air discharge temperature. The compressor clutch is cycled
off when the evaporator outlet air temperature falls below the
target value by at least a calibrated amount, and is thereafter
cycled on again when the evaporator outlet air temperature rises
above the target value. The target value is preferably biased to
prevent compressor operation when the desired air discharge
temperature exceeds outside air temperature by at least a
calibrated amount and to prevent the relative humidity in the
air-conditioned space from rising above a desired level.
Inventors: |
Kadle; Prasad S.;
(Williamsville, NY) ; Zima; Mark J.; (Clarence
Center, NY) |
Correspondence
Address: |
DELPHI TECHNOLOGIES, INC.
M/C 480-410-202, PO BOX 5052
TROY
MI
48007
US
|
Family ID: |
39708721 |
Appl. No.: |
11/805469 |
Filed: |
May 22, 2007 |
Current U.S.
Class: |
62/226 |
Current CPC
Class: |
B60H 2001/3245 20130101;
B60H 1/00735 20130101; B60H 2001/3275 20130101; B60H 1/3211
20130101; B60H 2001/3261 20130101; B60H 1/00835 20130101 |
Class at
Publication: |
62/226 |
International
Class: |
F25B 49/02 20060101
F25B049/02 |
Claims
1. A method of operation for an air conditioning system including a
variable displacement refrigerant compressor having a clutch that
is selectively activated and deactivated for turning the compressor
on and off and a pneumatic control valve for adjusting a pumping
capacity of the compressor in relation to its suction pressure, and
an evaporator that conditions inlet air for discharge into a
conditioned space, the method comprising the step of: determining a
target temperature for air exiting the evaporator; determining an
actual temperature of air exiting the evaporator; and deactivating
the clutch to turn off the compressor when the actual temperature
falls below the target temperature by at least a calibrated amount,
and then activating the clutch to turn on the compressor when the
actual temperature rises above the target temperature.
2. The method of claim 1, including the steps of: determining a
desired temperature of the air discharged into the conditioned
space; and determining the target temperature based on the desired
temperature.
3. The method of claim 1, including the steps of: determining a
desired temperature of the air discharged into the conditioned
space; and reducing the desired temperature by a calibrated amount
to form the target temperature.
4. The method of claim 1, including the steps of: determining a
first target temperature based on a desired temperature of the air
discharged into the conditioned space; determining a second target
temperature based on a temperature and desired relative humidity of
air in the conditioned space; and setting the target temperature
for air exiting the evaporator according to the lower of the first
and second target temperatures.
5. The method of claim 4, including the step of: setting the first
target temperature to a predetermined value when a temperature of
the inlet air is lower than the target temperature for air exiting
the evaporator by at least a calibrated amount.
6. A method of operation for a motor vehicle air conditioning
system including a variable displacement refrigerant compressor
having a clutch that is selectively activated and deactivated for
turning the compressor on and off and a pneumatic control valve for
adjusting a pumping capacity of the compressor in relation to its
suction pressure, an evaporator that chills inlet air passing
therethrough, and a heater core for selectively re-heating air
exiting the evaporator to satisfy a desired air discharge
temperature of the system, the method comprising the steps of:
detecting an over-capacity condition of the system for which the
pumping capacity of the compressor is such that series re-heating
of the air exiting the evaporator is required to satisfy the
desired air discharge temperature; and cyclically activating and
deactivating the clutch to cycle the compressor on and off while
the over-capacity condition is detected so as to satisfy the
desired air discharge temperature with a reduced compressor pumping
capacity.
7. The method of claim 6, including the steps of: determining a
target temperature for air exiting the evaporator based on the
desired air discharge temperature; and detecting the over-capacity
condition when a temperature of air exiting the evaporator falls
below the target temperature by at least a calibrated amount.
8. The method of claim 6, where the step of cyclically activating
and deactivating the clutch comprises the step of: deactivating the
clutch to turn off the compressor when the temperature of air
exiting the evaporator falls below the target temperature by at
least a calibrated amount, and then activating the clutch to turn
on the compressor when the temperature of air exiting the
evaporator rises above the target temperature.
9. The method of claim 6, where the air conditioning system is an
automatic climate control system, including a climate control
algorithm that develops said desired air discharge temperature and
a discharge air temperature control algorithm that regulates the
amount of air re-heated by the heater core to satisfy the desired
air discharge temperature.
10. The method of claim 6, where the air conditioning system is a
manual air conditioning system in which the desired air discharge
temperature is a user selected parameter, and the system includes a
discharge air temperature control that regulates the amount of air
re-heated by the heater core to satisfy the desired air discharge
temperature.
Description
TECHNICAL FIELD
[0001] The present invention relates to a motor vehicle air
conditioning system in which the capacity of a refrigerant
compressor is controlled for high efficiency, and more particularly
to a capacity control method for a variable displacement
refrigerant compressor in such an air conditioning system.
BACKGROUND OF THE INVENTION
[0002] Vehicle fuel efficiency studies have shown that a
traditional air conditioning system with a fixed displacement
compressor cycled on and off in the usual fashion can account for
the consumption of nearly twenty-five gallons of gasoline per
vehicle annually. As described in the U.S. Pat. No. 6,293,116 to
Forrest et al., however, air conditioning efficiency can be
significantly improved by regulating the compressor capacity in a
way that eliminates over-dehumidification and minimizes series
re-heating of conditioned air. Whereas compressor capacity is
traditionally regulated so as maximize cooling by the evaporator
without ice formation on the evaporator fins, the efficiency gains
described by Forrest et al. are achieved by regulating the
compressor capacity to provide a somewhat elevated evaporator
outlet air temperature (or refrigerant pressure) based on user
cooling and humidity requirements.
[0003] Simply applying the principles of Forrest et al. to a system
that cycles a fixed displacement compressor can result in a savings
of about six gallons of gasoline per vehicle annually, similar to
the savings that can be realized with a pneumatically controlled
variable displacement compressor. However, the savings can be most
dramatically increased--to nearly thirteen gallons of gasoline per
vehicle annually--by replacing the fixed displacement compressor
with an electronically controlled variable displacement compressor,
which is the approach preferred by Forrest et al. Nevertheless,
using an electronically controlled variable displacement compressor
usually results in higher overall system cost because of the
modulating control valve and the required control electronics.
Accordingly, what is needed is a way of achieving the fuel
efficiency obtainable with an electronically controlled system, but
at a lower cost.
SUMMARY OF THE INVENTION
[0004] The present invention provides an improved control
methodology for achieving an efficient compressor capacity control
with a pneumatically-controlled variable displacement compressor
and a compressor clutch that is selectively cycled on and off to
minimize series re-heating of conditioned air. Conditioned air is
discharged after passing through an evaporator core, and a target
value for the evaporator outlet air temperature is determined based
on the desired air discharge temperature. The compressor clutch is
cycled off when the evaporator outlet air temperature falls below
the target value by at least a calibrated amount, and is thereafter
cycled on again when the evaporator outlet air temperature rises
above the target value. The target value is preferably biased to
prevent compressor operation when the desired air discharge
temperature exceeds outside air temperature by at least a
calibrated amount and to prevent the relative humidity in the
air-conditioned space from rising above a desired level.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a diagram of an air conditioning system controlled
according to the present invention, including a
pneumatically-controlled variable displacement refrigerant
compressor with an electrically activated clutch, and a
microprocessor based controller.
[0006] FIG. 2 is a flow diagram of a control method carried out by
the controller of FIG. 1 according to this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0007] The present invention recognizes that the fuel efficiency
benefits described in the aforementioned U.S. Pat. No. 6,293,116 to
Forrest et al. can be achieved at a reduced system cost by
combining a pneumatically-controlled variable displacement
compressor (such as shown and described in the U.S. Pat. No.
4,428,718 to Skinner, for example) with a compressor clutch cycle
control that comes into play when series re-heating of the
conditioned air is required to achieve the desired air discharge
temperature. The system cost is reduced because a
pneumatically-controlled variable displacement compressor is less
expensive to produce than an electronically controlled variable
displacement compressor, and the control electronics required to
carry out the clutch cycling control are simpler and less expensive
than with traditional electronically controlled displacement.
Ordinarily, of course, a pneumatically-controlled variable
displacement compressor is not cycled on and off during activation
of the air conditioning system, but we have found that by doing so
to minimize series re-heating, the highest efficiency gains
obtainable by practicing the capacity control method described by
Forrest et al. can be very nearly achieved at a significantly lower
system cost. It is estimated that a system based on the present
invention will result in a fuel savings of approximately 11.5
gallons of gasoline per vehicle annually, compared to a system
using a traditionally controlled fixed displacement compressor.
[0008] The control method of this invention is illustrated
principally in the context of a motor vehicle climate control
system that automatically regulates heating, ventilating and air
conditioning (HVAC) parameters such as air discharge temperature,
air discharge location (mode), and blower speed. However, it should
be understood that the control can also be implemented in a
so-called manual system in which the user manually controls the air
discharge temperature and mode and the blower speed. Also, the
control can be implemented in a non-vehicular air conditioning
system if desired.
[0009] Referring FIG. 1, the reference numeral 10 generally
designates an automatic climate control system for a motor vehicle.
The system 10 includes a pneumatically-controlled variable
displacement refrigerant compressor 12 such as shown and described
in the aforementioned U.S. Pat. No. 4,428,718 to Skinner,
incorporated by reference herein. The compressor drive shaft is
coupled to a drive pulley 20 via an electrically activated clutch
22, and a drive belt (not shown) couples the drive pulley 20 to a
rotary drive source such as an engine accessory drive shaft so that
compressor 12 can be turned on and off by respectively engaging and
disengaging the clutch 22. The system 10 further includes a
condenser 24, an orifice tube 26, an evaporator 28, and an
accumulator/dehydrator 30 arranged in order between the discharge
and suction ports 16 and 18 of compressor 12. The cooling fans 32
are electrically activated to provide supplemental airflow for
removing heat from high-pressure refrigerant in condenser 24. The
orifice tube 26 allows the cooled high-pressure refrigerant in line
34 to expand in isenthalpic fashion before passing through the
evaporator 28. The accumulator/dehydrator 30 separates low-pressure
gaseous and liquid refrigerant, directs gaseous refrigerant to the
compressor suction port 18, and stores excess refrigerant that is
not in circulation. In an alternative system configuration, the
orifice tube 26 is replaced with a thermostatic expansion valve
(TXV); in this case, the accumulator/dehydrator 30 is omitted, and
a receiver/drier (R/D) is inserted in line 34 upstream of the TXV
to ensure that sub-cooled liquid refrigerant is available at the
TXV inlet.
[0010] The evaporator 28 is formed as an array of finned
refrigerant-conducting tubes, and an air intake duct 36 disposed on
one side of evaporator 28 houses a motor driven ventilation blower
38 for forcing air past the evaporator tubes. The duct 36 is
divided upstream of the blower 38, and an inlet air control door 40
is adjustable as shown to control inlet air mixing. Depending on
the position of air control door 40, outside air may enter blower
38 through duct leg 42, and cabin air may enter blower 38 through
duct leg 44.
[0011] An air outlet duct 46 disposed on the downstream side of
evaporator 24 houses a heater core 48 formed as an array of finned
tubes through which flows engine coolant. The heater core 48
effectively divides the outlet duct 46, and a re-heat door 50 next
to heater core 48 is adjustable as shown to apportion the airflow
through and around heater core 48. The heated and un-heated air
portions are mixed in a plenum 52 downstream of re-heat door 50,
and two discharge air control doors 54 and 56 are adjustable as
shown to direct the mixed air through one or more outlets,
including a defrost outlet 58, a heater outlet 60, and driver and
passenger panel outlets 62 and 64.
[0012] As described in detail in the aforementioned U.S. Pat. No.
4,428,718 to Skinner, the compressor 12 is equipped with a
pneumatically activated control valve 14 that adjusts the
compressor displacement, and therefore its pumping capacity, in
response to both the discharge (outlet) pressure at discharge port
16 and the suction (inlet) pressure at suction port 18. In general,
the control valve 14 adjusts the compressor capacity to full
displacement upon activation of compressor clutch 22, and
thereafter reduces the displacement when the suction pressure
indicates that the evaporator temperature is approaching a value
(such as 4.degree. C.) just sufficient to prevent condensate from
freezing on the fins of evaporator 28. As explained below, however,
the control of the present invention overrides the capacity control
of control valve 14 under specified conditions to reduce the
effective compressor capacity by cycling the compressor clutch 22
on and off.
[0013] Referring again to FIG. 1, the reference numeral 70
designates a microprocessor-based controller for carrying out
compressor capacity control of the present invention, as well as
the traditional automatic climate control functions. Accordingly,
the controller 70 regulates the operation of the compressor clutch
22, the cooling fans 32, the blower 38, and the various air control
doors 40, 50, 54 and 56. The control is carried out in response to
various system-related and vehicle-related inputs which are
generally designated by the reference numeral 72. A system-related
input especially pertinent to the control of the present invention
is the evaporator outlet air temperature (EOAT) on line 74, as
measured by a thermistor 76 disposed just downstream of the
evaporator 28.
[0014] FIG. 2 is a diagram illustrating a control carried out by
the controller 70 of FIG. 1 according to the present invention. The
reference numeral 80 designates a conventional automatic climate
control algorithm (ACCA) that determines target values for the
blower speed, and the air discharge temperature and mode based on
various inputs including the user set temperature (SET), the cabin
air temperature (CAT), the outside air temperature (OAT), and a
measure of solar loading (SOLAR). The target blower speed (BStar)
is supplied to a blower speed control algorithm (BSCA) 82 that
activates the electric motor of blower 38; the target discharge
mode (DMtar) is supplied to a discharge mode control algorithm
(DMCA) 84 that activates the discharge air control doors 54 and 56;
and the target discharge air temperature (DATtar) is supplied to a
discharge air temperature control algorithm (DATCA) 86 that
activates the re-heat air control door 50. The control algorithms
82 and 84 usually involve simple open-loop control strategies,
while the control algorithm 86 frequently involves a closed-loop
control strategy in which re-heat air control door 50 is adjusted
based on the deviation of the actual (measured) discharge air
temperature from the target value DATtar.
[0015] Blocks 88-104 describe a control according to the present
invention for cycling the compressor clutch 22 on and off
(effectively overriding the compressor capacity control of
pneumatic control valve 14) under certain operating conditions for
improved system efficiency. The control is based on the measured
evaporator outlet air temperature EOAT and the target discharge air
temperature DATtar, and activates cycling of the compressor clutch
22 when EOAT is lower than required to satisfy DATtar. In a
traditional system, the controller 70 maintains activation of
compressor clutch 22 so long as the outside air temperature is
above a minimum value, and the discharge air temperature control
algorithm DATCA 86 satisfies the target value DATtar by positioning
re-heat air control door 50 so that some or all of the air exiting
evaporator 28 passes through the heater core 48. But when the
compressor clutch 22 is cycled on and off according to the present
invention, the discharge air temperature will more nearly match
DATtar, allowing the discharge air temperature control algorithm
DATCA 86 to satisfy DATtar with little or no series re-heating of
the air exiting evaporator 28.
[0016] When the described control is implemented on a manual air
conditioning system, the target value DATtar can be a temperature
that is based on the position of a user-manipulated temperature
control lever. In other words, the temperature control lever only
provides a desired discharge air temperature, and a control
algorithm such as the discharge air temperature control algorithm
(DATCA) 86 is provided for adjusting the re-heat air control door
50 as required to satisfy the desired temperature.
[0017] Blocks 88-92 determine a temperature-based target
(EOATtar_temp) for the evaporator outlet air temperature. Block 88
compares the outside air temperature OAT with a difference
(DATtar-CALtemp) that represents the evaporator outlet air
temperature required to satisfy DATtar. Accordingly, the term
CALtemp is a calibrated value that represents the typical rise in
air temperature (2.degree. C., for example) between the outlet of
evaporator 28 and the air outlets 58-64. If (DATtar-CALtemp) is
higher than OAT, DATtar can be achieved with compressor 12 turned
off, and block 90 sets the EOATtar_temp to an artificially high
value such as 100.degree. C. If (DATtar-CALtemp) less than or equal
to OAT, at least some compressor operation will be required to
achieve DATtar, and block 92 sets the EOATtar_temp to the
difference (DATtar-CALtemp).
[0018] Block 94 determines a humidity-based target (EOATtar_hum)
for the evaporator outlet air temperature. As explained in the
aforementioned U.S. Pat. No. 6,293,116 to Forrest et al., the
evaporator outlet air temperature required to prevent the relative
humidity in the cabin from rising above a desired level can be
achieved by calculation or table look-up as a function of the
measured cabin air temperature CAT (or set temperature SET) and the
desired relative humidity RHdes.
[0019] Block 96 sets the evaporator outlet air temperature target
EOATtar equal to the lesser of EOATtar_temp and EOATtar_hum, as
indicated by the MIN function. Under most conditions, EOATtar_temp
will be less than EOATtar_hum, and EOATtar will be set to a
temperature designed to achieve DATtar. However, in cases where
additional compressor capacity is required to prevent the cabin air
from becoming too humid for occupant comfort, EOATtar_hum will be
less than EOATtar_temp; in this case, EOATtar will be set to a
temperature somewhat lower than required to achieve DATtar, and the
discharge air temperature control algorithm DATCA 86 will adjust
re-heat air control door 50 for series re-heating of the air
exiting evaporator 28. The humidity-based target EOATtar_hum also
comes into play when the outside air temperature OAT is less than
the difference (DATtar-CALtemp), and block 90 sets the EOATtar_temp
to 100.degree. C.
[0020] Blocks 98-104 control activation of the compressor clutch 22
based on the target value EAOTtar determined at block 96. Block 98
compares the measured value EOAT with EOATtar, while block 100
compares EOAT with the difference (EOATtar-CALhys), where CALhys is
a calibrated temperature delta that provides cycling hysteresis.
The compressor clutch 22 will be activated initially, and blocks
100 and 102 deactivate clutch 22 for capacity control if EOAT falls
below the difference (EOATtar-CALhys). Turning off the compressor
12 will allow EOAT to rise toward the inlet air temperature, and
blocks 98 and 104 re-activate compressor clutch 22 when EOAT rises
above EOATtar. In practice, CALhys is calibrated high enough to
avoid rapid cycling of the compressor 12, but low enough to prevent
noticeable temperature swings in the cabin.
[0021] In summary, the control method of the present invention
provides a novel approach for achieving highly efficient climate
control with a climate control system built around a low-cost
pneumatically controlled variable displacement compressor. While
the present invention has been described with respect to the
illustrated embodiment, it is recognized that numerous
modifications and variations in addition to those mentioned herein
will occur to those skilled in the art. Accordingly, it is intended
that the invention not be limited to the disclosed embodiment, but
that it have the full scope permitted by the language of the
following claims.
* * * * *