U.S. patent application number 10/578462 was filed with the patent office on 2007-05-03 for air-conditioning assembly.
Invention is credited to Jin Ming Liu.
Application Number | 20070095085 10/578462 |
Document ID | / |
Family ID | 34531261 |
Filed Date | 2007-05-03 |
United States Patent
Application |
20070095085 |
Kind Code |
A1 |
Liu; Jin Ming |
May 3, 2007 |
Air-Conditioning Assembly
Abstract
The invention relates to a motor vehicle air-conditioning
assembly provided with a supercritical fluid refrigerant circuit
and comprising a pressure relief member (12) defining a
cross-section of fluid flow. The assembly comprises an electronic
control device (401) for interacting with the fluid refrigerant
circuit. The electronic control device includes a computing
function using an estimation of the cross-section of flow of the
pressure relief member, the density coefficient of the fluid
refrigerant, and the pressure of the fluid refrigerant at the inlet
of the pressure relief member for calculating an estimation of the
mass flow rate of the fluid refrigerant in the pressure relief
member (12).
Inventors: |
Liu; Jin Ming; (Honorine,
FR) |
Correspondence
Address: |
Valeo Climate Control;Intellectual Property Department Corp.
4100 North Atalntic Boulevard
Auburn
MI
48326
US
|
Family ID: |
34531261 |
Appl. No.: |
10/578462 |
Filed: |
November 17, 2004 |
PCT Filed: |
November 17, 2004 |
PCT NO: |
PCT/IB04/03769 |
371 Date: |
May 8, 2006 |
Current U.S.
Class: |
62/222 ;
62/228.1; 62/228.3 |
Current CPC
Class: |
F25B 2500/19 20130101;
F25B 2600/17 20130101; B60H 1/3205 20130101; B60H 2001/3254
20130101; F25B 9/008 20130101; B60H 2001/3263 20130101; F25B
2309/061 20130101; F25B 2341/063 20130101; F25B 2700/13 20130101;
F25B 41/31 20210101; B60H 2001/3285 20130101 |
Class at
Publication: |
062/222 ;
062/228.1; 062/228.3 |
International
Class: |
F25B 41/04 20060101
F25B041/04; F25B 49/00 20060101 F25B049/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 25, 2003 |
FR |
03/13823 |
Claims
1. A motor vehicle air conditioning unit, provided with a
supercritical refrigerant circuit (10) comprising a compressor
(14), a gas cooler (11), an expander (12), defining a refrigerant
flow area, and an evaporator (13), the assembly further including
an electronic control device designed to interact with the
refrigerant circuit, characterized in that the electronic control
device includes a calculating function using an estimate of the
flow area of the expander, the density (.rho.) of the refrigerant
and the pressure (P.sub.20) of the refrigerant at the inlet of the
expander in order to calculate an estimate of the refrigerant mass
flow rate (m.sub.exp) at the expander.
2. The air conditioning unit as claimed in claim 1, characterized
in that the flow area of the expander is estimated from the value
of the refrigerant pressure (P.sub.20) at the inlet of the
expander.
3. The air conditioning unit as claimed in claim 2, characterized
in that the electronic control device is capable of reacting to the
fact that the value of the refrigerant pressure P.sub.20 at the
inlet of the expander is: less than or equal to a first pressure
value P1, a first constant S1 being assigned to the flow area S of
the expander; less than or equal to a second pressure value P2
greater than the first pressure value P1, by solving the following
equation in order to calculate an estimate of the flow area S of
the expander: S=S1+(S2-S1).times.(P.sub.20-P1)/(P2-P1), where S2 is
a second constant; less than or equal to a third pressure value P3
less than or equal to a third pressure value P3 and greater than
the second pressure value P2, solving the following equation in
order to calculate an estimate of the flow area S of the expander:
S=S2+(S3-S2).times.(P.sub.20-P2)/(P3-P2), where S3 is a third
constant; and greater than or equal to the third pressure value P3,
a fourth constant S4 being assigned to the flow area of the
expander.
4. The air conditioning unit as claimed in claim 3, characterized
in that the first pressure value P1 is approximately equal to 80
bar, the second pressure value P2 is approximately equal to 110 bar
and the third pressure value P3 is approximately equal to 135 bar
and in that the first constant S1 is approximately equal to 0.07
mm.sup.2, the second constant S2 is approximately equal to 0.5
mm.sup.2, the third constant S3 is approximately equal to 0.78
mm.sup.2 and the fourth constant S4 is approximately equal to 3.14
mm.sup.2.
5. The air conditioning unit as claimed in one of the preceding
claims, characterized in that the calculating function is specific
to calculating the density (.rho.) of the refrigerant from the
refrigerant temperature (T.sub.30) at the inlet of the expander and
from the refrigerant pressure (P.sub.20) at the inlet of the
expander.
6. The air conditioning unit as claimed in claim 5, characterized
in that it includes a probe (30) placed at the inlet of the
expander (12) for measuring the refrigerant temperature (T.sub.30)
at the inlet of the expander.
7. The air conditioning unit as claimed in one of the preceding
claims, characterized in that it includes a sensor (20) placed at
the inlet of the expander (12) for measuring the refrigerant
pressure (P.sub.20) at the inlet of the expander.
8. The air conditioning unit as claimed in one of the preceding
claims, characterized in that the electronic control device further
includes a power estimation function capable of estimating the
power absorbed by the compressor from: the refrigerant mass flow
rate (m.sub.exp) provided by the calculating function; the work
(.DELTA.Hise) of the compressor; and the rotation speed (N) of the
compressor.
9. The air conditioning unit as claimed in claim 8, characterized
in that the electronic control device is capable of estimating the
work (.DELTA.Hise) of the compressor from the refrigerant pressure
(P.sub.20) at the inlet of the expander, from the refrigerant
pressure (P.sub.35) at the inlet of the compressor and from a
refrigerant temperature (T.sub.comp) relative to the
compressor.
10. The air conditioning unit as claimed in claim 9, characterized
in that the refrigerant pressure (P.sub.35) at the inlet of the
compressor is estimated from a pressure (P.sub.50) at the inlet or
at the outlet of the evaporator (13) combined with the refrigerant
mass flow rate (m.sub.exp).
11. The air conditioning unit as claimed in claim 10, characterized
in that the pressure (P.sub.50) at the inlet or at the outlet of
the evaporator (13) is determined from the refrigerant temperature
(T.sub.50) at the inlet or at the outlet of the evaporator (13),
said temperature being either measured by a probe or estimated
from: a temperature (T.sub.40) relative to the evaporator (13); the
efficiency (.eta..sub.evap) of the evaporator (13); and the
temperature (T.sub.60) of the air to be cooled.
12. The air conditioning unit as claimed in one of claims 9 to 11,
characterized in that the refrigerant temperature relative to the
compressor (10) is the refrigerant temperature (T.sub.35) at the
inlet of the compressor.
13. The air conditioning unit as claimed in claim 12, characterized
in that it includes a probe (35) placed at the inlet of the
compressor (14) for measuring the refrigerant temperature
(T.sub.35) at the inlet of the compressor.
14. The air conditioning unit as claimed in one of claims 9 to 11,
characterized in that the refrigerant temperature relative to the
compressor (14) is the refrigerant temperature (T.sub.36) at the
outlet of the compressor.
15. The air conditioning unit as claimed in claim 14, characterized
in that it includes a probe (36) placed at the outlet of the
compressor (14) for measuring the refrigerant temperature
(T.sub.36) at the outlet of the compressor.
Description
[0001] The invention relates to motor vehicle air conditioning
circuits.
[0002] In conventional motor vehicles, the compressor of the air
conditioning circuit is driven by the engine and therefore consumes
part of the engine's power. The power absorbed by the compressor,
when it is operating, reduces the efficiency of the engine and
consequently increases the fuel consumption and the pollution
generated by the exhaust gases from the vehicle. This drawback is
problematic in the case of mechanical compressors with an external
control, the use of which is commonplace.
[0003] Moreover, in existing constructions, the fuel injection
computer of the vehicle does not have the instantaneous value of
the actual power absorbed by the compressor and therefore chooses,
for the operation of the compressor, fuel injection parameters by
default, which correspond to the maximum value of the power
absorbed, which value is rarely reached in practice.
[0004] Consequently, one solution for optimizing the efficiency of
the engine consists in estimating the instantaneous value of this
power actually absorbed by the compressor. When this information is
known, it is then possible to adapt the fuel injection parameters
of the engine to the actual requirements.
[0005] In existing constructions, an estimate of the refrigerant
mass flow rate is used to calculate the instantaneous power
absorbed by the compressor.
[0006] Such constructions generally involving subcritical
refrigerants are unsuitable for supercritical refrigerants.
[0007] The use of supercritical refrigerants, especially the
CO.sub.2 refrigerant R744, was developed for vehicle air
conditioning circuits in order to limit the deleterious effects of
refrigerants on the environment. The CO.sub.2 refrigerant has a
much smaller global warming effect than subcritical refrigerants,
such as the HFC refrigerants of the R134a type.
[0008] An air conditioning circuit using a supercritical fluid
comprises a compressor, a gas cooler, an internal heat exchanger,
an expander and an evaporator, the refrigerant passing through
these in the above order. In such a circuit, the cooling of the
refrigerant after compression undergoes no phase change. The
refrigerant passes into the liquid state only during the expansion.
This property of supercritical fluids means that the assembly given
in patent application 01/16568 cannot be used to estimate the
supercritical refrigerant flow rate and the power consumed by the
compressor.
[0009] US 2003/0115896 A1 proposes an air conditioning unit for
estimating the mass flow rate of a supercritical refrigerant, based
on a measurement of the high pressure and a measurement of the low
pressure. However, in order for the estimate for the mass flow rate
to be sufficiently accurate, it is necessary for the air
conditioning circuit to be controlled so that the refrigerant
leaving the expander is almost entirely in the liquid state.
Moreover, a sensor is required for measuring the low pressure,
which increases the cost of the air conditioning unit.
[0010] French patent application 03/03362 also proposes an air
conditioning unit for estimating the mass flow rate of a
supercritical refrigerant. To do this, the proposed air
conditioning unit includes a calculating function that uses two
differences in temperature relating to the gas cooler, at least one
of which is based on the temperature of the refrigerant at a chosen
intermediate point on the gas cooler. This intermediate point is in
particular located at a distance x.sub.i from the inlet of the gas
cooler that is between 5% and 35% of the total length of the gas
cooler. However, this assembly requires a large number of sensors
(sensors for measuring the refrigerant pressure at the inlet and
outlet of the compressor, the temperature of the refrigerant at the
inlet of the gas cooler, the temperature of the stream of air
received by the gas cooler and the temperature of the refrigerant
at the chosen intermediate point on the gas cooler), which
therefore increases the cost of the assembly.
[0011] The subject of the present invention is an air conditioning
unit that remedies these known drawbacks of the prior art.
[0012] For this purpose, the invention proposes a motor vehicle air
conditioning unit, provided with a supercritical refrigerant
circuit comprising a compressor, a gas cooler, an expander,
defining a refrigerant flow area, and an evaporator. The assembly
further includes an electronic control device designed to interact
with the refrigerant circuit. Advantageously, the electronic
control device includes a calculating function using an estimate of
the flow area of the expander, the density of the refrigerant and
the pressure of the refrigerant at the inlet of the expander in
order to calculate an estimate of the refrigerant mass flow rate at
the expander.
[0013] According to one aspect of the invention, the flow area of
the expander is estimated from the refrigerant pressure at the
inlet of the expander.
[0014] In particular, the electronic control device may be capable
of reacting to the fact that the value of the refrigerant pressure
P.sub.20 at the inlet of the expander is: [0015] less than or equal
to a first pressure value P1, a first constant S1 being assigned to
the flow area of the expander; [0016] less than or equal to a
second pressure value P2 greater than the first pressure value P1,
by solving the following equation in order to calculate an estimate
of the flow area S of the expander:
S=S1+(S2-S1).times.(P.sub.20-P1)/(P2-P1), [0017] where S2 is a
second constant; [0018] less than or equal to a third pressure
value P3 and greater than the second pressure value P2, solving the
following equation in order to calculate an estimate of the flow
area S of the expander: S=S2+(S3-S2).times.(P.sub.20-P2)/(P3-P2),
[0019] where S3 is a third constant; and [0020] greater than or
equal to the third pressure value P3, a fourth constant S4 being
assigned to the flow area of the expander.
[0021] In one particular embodiment, the first pressure value P1 is
approximately equal to 80 bar, the second pressure value P2 is
approximately equal to 110 bar and the third pressure value P3 is
approximately equal to 135 bar, while the first constant S1 is
approximately equal to 0.07 mm.sup.2, the second constant S2 is
approximately equal to 0.5 mm.sup.2, the third constant S3 is
approximately equal to 0.78 mm.sup.2 and the fourth constant S4 is
approximately equal to 3.14 mm.sup.2.
[0022] According to another aspect of the invention, the
calculating function is specific to calculating the density of the
refrigerant from the refrigerant temperature at the inlet of the
expander and from the refrigerant pressure at the inlet of the
expander.
[0023] The air conditioning unit may include a probe placed at the
inlet of the expander for measuring the refrigerant temperature at
the inlet of the expander.
[0024] The air conditioning unit may also include a sensor placed
at the inlet of the expander for measuring the refrigerant pressure
at the inlet of the expander.
[0025] As a complement, the electronic control device may include a
power estimation function capable of estimating the power absorbed
by the compressor from: [0026] the refrigerant mass flow rate
provided by the calculating function; [0027] the work of the
compressor; and [0028] the rotation speed of the compressor.
[0029] The electronic control device is capable of estimating the
work of the compressor from the refrigerant pressure at the inlet
of the expander, from the refrigerant pressure at the inlet of the
compressor and from a refrigerant temperature relative to the
compressor.
[0030] Advantageously, the refrigerant pressure at the inlet of the
compressor is estimated from a pressure at the inlet or at the
outlet of the evaporator combined with the refrigerant mass flow
rate.
[0031] Furthermore, the pressure at the inlet or at the outlet of
the evaporator is determined from the refrigerant temperature, said
temperature being either measured by a probe or estimated from:
[0032] a temperature relative to the evaporator; [0033] the
efficiency of the evaporator; and [0034] the temperature of the air
to be cooled.
[0035] The refrigerant temperature relative to the compressor may
be the refrigerant temperature at the inlet of the compressor.
[0036] The air conditioning unit may then include a probe placed at
the inlet of the compressor for measuring the refrigerant
temperature at the inlet of the compressor.
[0037] As a variant, the refrigerant temperature relative to the
compressor may be the refrigerant temperature at the outlet of the
compressor.
[0038] The air conditioning installation may then include a probe
placed at the outlet of the compressor for measuring the
refrigerant temperature at the outlet of the compressor.
[0039] The invention also covers a product-program, which may be
defined as comprising the functions used for estimating the
refrigerant mass flow rate and the power consumed by the
compressor.
[0040] Other features and advantages of the invention will become
apparent on examining the detailed description below and the
appended drawings in which:
[0041] FIG. 1A is a diagram of a motor vehicle air conditioning
circuit operating with a supercritical refrigerant;
[0042] FIG. 1B is a diagram of an air conditioning unit according
to the invention;
[0043] FIG. 2 is a plot showing the variations in the flow area of
the expander as a function of the refrigerant pressure at the inlet
of the expander;
[0044] FIG. 3 is a flow diagram showing the steps implemented by
the control device for estimating the refrigerant mass flow rate at
the expander;
[0045] FIG. 4 is a flow diagram showing the steps implemented by
the control device for estimating the flow area of the
expander;
[0046] FIG. 5 is a flow diagram representing the steps implemented
by the control device for estimating the power consumed by the
compressor, according to the invention;
[0047] FIGS. 6 and 7 are diagrams of the air conditioning circuit
according to alternative embodiments of the invention;
[0048] FIGS. 8 to 12 are schematic diagrams showing the position of
the temperature probes used for determining the pressure at the
inlet or at the outlet of the evaporator;
[0049] FIG. 13 illustrates the method of determining the pressure
of the refrigerant at the inlet of the compressor; and
[0050] FIG. 14 shows the relationship between the refrigerant mass
flow rate and the refrigerant pressure at the inlet of the
compressor.
[0051] Appendix A comprises the main mathematical equations used
for implementing the assembly.
[0052] The drawings essentially contain elements having a certain
character. They therefore serve not only for making the description
more clearly understood but also for contributing to the definition
of the invention, where appropriate.
[0053] FIG. 1A represents an air conditioning circuit through which
a supercritical refrigerant flows. Hereafter, the description will
refer to the supercritical refrigerant CO.sub.2 as a nonlimiting
example.
[0054] Such a circuit conventionally comprises: [0055] a compressor
14 suitable for receiving the refrigerant in the gaseous state and
compressing it; [0056] a gas cooler 11 suitable for cooling the gas
compressed by the compressor; [0057] an expander 12 suitable for
lowering the pressure of the refrigerant; and [0058] an evaporator
13 suitable for making the refrigerant from the expander pass from
the liquid state to the gaseous state in order to produce a stream
of conditioned air 21 that is sent into the passenger compartment
of the vehicle.
[0059] The circuit may further include an internal heat exchanger
23, allowing the refrigerant flowing from the gas cooler to the
expander to give up heat to the refrigerant flowing from the
evaporator to the compressor. The circuit may further include an
accumulator 17 placed between the outlet of the evaporator and the
inlet of the compressor, in order to avoid liquid surges.
[0060] The gas cooler 11 receives a stream of external air 16 for
extracting the heat taken from the passenger compartment, which
stream under certain operating conditions is blown by a motor/fan
unit 15.
[0061] The evaporator 13 receives a stream of air from a blower, in
order to produce a stream of conditioned air 21.
[0062] The expander 12 may have a variable flow area, such as an
electronic expander, a thermostatic expander or any other expander
for which the flow area depends on the high pressure. The expander
12 may also have a fixed flow area, such as a calibrated
orifice.
[0063] The supercritical refrigerant is compressed in the gaseous
phase and raised to a high pressure by the compressor 14. The gas
cooler 11 then cools the refrigerant by means of the incoming
stream of air 16. Unlike the air conditioning circuits operating
with a subcritical refrigerant, the cooling of the refrigerant
after compression does not involve a phase change. The refrigerant
passes to the two-phase state, with a vapor content that depends on
the low pressure, only during the expansion. The internal heat
exchanger 23 allows the refrigerant to be very strongly cooled.
[0064] Referring now to FIG. 1B, this shows an air conditioning
unit according to the invention installed in a motor vehicle.
[0065] The motor vehicle is driven by an engine 43, which may be
controlled by a fuel injection computer 42. The fuel injection
computer 42 receives information from various sensors, which it
interprets in order to adjust the injection parameters.
[0066] The fuel injection computer 42 may also provide information
about the conditions inside or outside the vehicle (information
provided by a solar sensor, number of occupants, etc.). In
particular, it may provide information about instantaneous values
relating to the operation of the vehicle, and especially about the
rotational speed N of the compressor.
[0067] The unit is also provided with an air conditioning computer
40, comprising a passenger compartment regulator 41 and an air
conditioning loop regulator 402. The passenger compartment
regulator 41 is designed to set the temperature setpoint of the
external air blown into the evaporator 13.
[0068] The engine fuel injection computer may act on the air
conditioning unit via an air conditioning regulator 402. This link
may prevent the operation of the air conditioning unit when the
engine is on high load.
[0069] The air conditioning unit according to the invention is
based on a model of the expander, in order to provide an estimate
of the refrigerant mass flow rate m.sub.exp at the expander.
[0070] The air conditioning unit includes an electronic control
device, for example an electronic card 401, designed to interact
with the air conditioning circuit 10 via the links 30/31 and with
the fuel injection computer 42 via the links 32/33.
[0071] The electronic card 401 may be considered as an integral
part of the vehicle air conditioning computer 40.
[0072] The electronic card 401 may receive information 30 coming
from sensors fitted on the air conditioning circuit 10. It may also
receive information from the engine fuel injection computer 42 via
the link 33, in particular the rotation speed N of the compressor
and/or the run speed V of the vehicle.
[0073] The Applicant has found that the expander may be modelled by
equation A10 of Appendix A, where K is a coefficient that
characterizes the expander, in particular its pressure drop.
[0074] From this model, the calculating function can calculate an
estimate of the refrigerant mass flow rate m.sub.exp at the
expander from: [0075] the pressure P.sub.20 of the refrigerant at
the inlet of the expander; [0076] the density .rho. of the CO.sub.2
refrigerant; and [0077] the flow area S (in mm.sup.2) of the
expander.
[0078] The Applicant has also found that the density .rho. of the
CO.sub.2 refrigerant may be estimated from the temperature T.sub.30
at the inlet of the expander and from the pressure P.sub.20 at the
inlet of the expander, according to equation A11 of Appendix A.
[0079] The Applicant has furthermore found that the flow area S (in
mm.sup.2) of an expander with a flow area depends on the
refrigerant pressure P.sub.20 at the inlet of the expander.
[0080] Thus, an estimate of the refrigerant mass flow rate
m.sub.exp at the expander may be obtained from the refrigerant
pressure P.sub.20 at the inlet of the expander and from the
temperature T.sub.30 at the inlet of the expander.
[0081] The refrigerant pressure P.sub.20 at the inlet of the
expander and the refrigerant temperature T.sub.30 at the inlet of
the expander may be estimated or measured.
[0082] The air conditioning circuit may include two separate
sensors for measuring the refrigerant pressure P.sub.20 at the
inlet of the expander and the refrigerant temperature T.sub.30 at
the inlet of the expander, respectively. As a variant, the air
conditioning circuit may have a single sensor placed at the inlet
of the expander for measuring both these quantities.
[0083] FIG. 2 is a plot showing the variation in the flow area S
(in mm.sup.2) as a function of the refrigerant pressure P.sub.20
(in bar) at the inlet of the expander. The curves shown on this
plot correspond to equations A2 to A5 of Appendix A.
[0084] As long as the refrigerant pressure P.sub.20 at the inlet of
the expander is less than or equal to a first pressure value P1,
the area S is equal to a first constant S1 according to equation A2
of Appendix A.
[0085] When the pressure P.sub.20 is above the first pressure value
P1 and less than or equal to a second pressure value P2, the area S
follows a straight line whose directrix is determined from the
values of S1, P1, P2 and a second constant S2, in accordance with
equation A3 of Appendix A. The value of S2 corresponds to the value
of the area S when P.sub.20 is equal to the valave P2.
[0086] When the pressure P.sub.20 is greater than the second
pressure value P2 and less than or equal to a third pressure value
P3, the area S follows a straight line whose directrix is
determined from the values of S2, P2, P3 and a third constant S3 in
accordance with equation A4 of Appendix A.
[0087] When the pressure P.sub.20 is greater than or equal to the
third pressure value P3, the area S is equal to a fourth constant
S4 greater than the third constant S3 in accordance with equation
A5 of Appendix A.
[0088] In particular, the first pressure value P1 may be
approximately equal to 80 bar, the second pressure value P2 may be
approximately equal to 110 bar, the third pressure value P3 may be
approximately equal to 135 bar, the first constant S1 may be
approximately equal to 0.07 mm.sup.2, the second constant S2 may be
approximately equal to 0.5 mm.sup.2, the third constant S3 may be
approximately equal to 0.78 mm.sup.2 and the fourth constant S4 may
be approximately equal to 3.14 mm.sup.2.
[0089] As a complement, the estimate of the refrigerant mass flow
rate, provided by the calculating function of the electronic card,
may be used to calculate the mechanical power absorbed. To do this,
the electronic card includes a power estimation function capable of
estimating the power P.sub.abs absorbed by the compressor from the
refrigerant mass flow rate m.sub.exp. In particular, the power
estimation function is capable of estimating the power P.sub.abs
absorbed by the compressor from the isentropic work of compression
W.sub.ise and from the rotation speed N of the compressor in
accordance with equation A6 of Appendix A. The coefficients a and b
are related to operating parameters of the air conditioning
circuit. The coefficient a corresponds to the mechanical efficiency
relative to the isentropic compression of the compressor and is
around 1.38. The coefficient b is the image of the compressor
efficiency and corresponds to the friction factor of the
compressor.
[0090] In accordance with equation A7 of Appendix A, the isentropic
compression power W.sub.ise is related: [0091] to the refrigerant
mass flow rate m.sub.exp, an estimate of which is calculated by the
calculating function as described above; and [0092] to the
isentropic work .DELTA.H.sub.ise of the compressor.
[0093] The Applicant has found that the estimate of the work
.DELTA.H.sub.ise of the compressor may be obtained, in accordance
with equation A80 of Appendix A, from: [0094] the refrigerant
pressure P.sub.20 at the inlet of the expander; [0095] the
refrigerant pressure P.sub.35 at the inlet of the compressor; and
[0096] the temperature of the refrigerant T.sub.comp relative to
the compressor.
[0097] The refrigerant pressure P.sub.35 at the inlet of the
compressor and the temperature of the refrigerant T.sub.comp
relative to the compressor may be estimated or measured.
[0098] The pressure of the refrigerant at the inlet of the
compressor is estimated using the refrigerant mass flow rate
m.sub.exp calculated above and from the pressure drop .DELTA.p
between the inlet of the evaporator 13 and the inlet of the
compressor 14.
[0099] As a variant, this estimate of the refrigerant pressure at
the inlet of the compressor may be determined using the refrigerant
mass flow rate m.sub.exp calculated above and from the pressure
drop .DELTA.p between the outlet of the evaporator 13 and the inlet
of the compressor 14.
[0100] The example below is described in relation to the inlet
pressure of the evaporator 13, but this example can be transposed
in a similar manner using the pressure at the outlet of the
evaporator 13.
[0101] This pressure drop .DELTA.p is calculated from formula A90
of Appendix A, in which: [0102] P.sub.50 is an estimate of the
pressure at the inlet of the evaporator; [0103] P.sub.35 is the
estimate of the refrigerant pressure at the inlet of the
compressor.
[0104] It is also known that this pressure drop .DELTA.p may be
determined from formula A100 in which: [0105] K is a pressure drop
coefficient; [0106] .rho. is the density of the refrigerant; and
[0107] V.sub.co.sub.2 is the speed of the refrigerant.
[0108] In accordance with equation A101 of Appendix A, the speed of
the refrigerant V.sub.co.sub.2 can be determined from: [0109] the
refrigerant mass flow rate m.sub.exp determined by means of
equation A10; [0110] the refrigerant density .rho.; and [0111] a
constant S corresponding to the mean flow area and mean flow
length, combining both the linear pressure drop and the singular
pressure drop, experienced by the refrigerant. From the two
equations A90 and A100 it is possible to estimate the pressure of
the refrigerant at the inlet of the compressor, as illustrated by
equation A9.
[0112] Thus, the only unknown in this equation is the estimate of
the pressure P.sub.50 at the inlet of the evaporator.
[0113] It is known from the fluids saturation law, otherwise known
as the fluid state law, that the pressure P.sub.50 at the inlet of
the evaporator depends directly on the saturation temperature
T.sub.50 at the inlet of the evaporator. Over the operating range
of interest to us, this equation may be represented in the form of
a second-order polynomial.
[0114] This saturation temperature T.sub.50 of the pressure
refrigerant may be measured or estimated.
[0115] When it is estimated, equation A91 of Appendix A is used, in
which: [0116] T.sub.40 is a datum relating to the evaporator
temperature available on many air conditioning units. This involves
a CTN or CTP probe placed on the evaporator, the main objective of
which in the prior art is to prevent the evaporator from icing up
when the compressor stops. This temperature T.sub.40 corresponds to
the surface temperature of one of the walls of the evaporator 13
(for example at the recess of the inserts, as illustrated in FIG.
12) or to the air temperature at the outlet of the evaporator;
[0117] .eta..sub.evap is the image of the evaporator efficiency,
which can be easily related to a function of the voltage U for the
air blower of the evaporator in the passenger compartment and the
run speed V of the vehicle, as expressed in equation A910 of
Appendix A; and [0118] T.sub.60 is the temperature of the air to be
cooled by the air conditioning unit. This temperature is estimated
according to the temperature inside the passenger compartment, the
temperature outside the passenger compartment, the voltage U for
the blower, the position of the recycling flap of the air
conditioning unit and the run speed V of the vehicle. This function
is expressed in equation A920 of Appendix A.
[0119] FIGS. 8 and 9 illustrate the possibility of measuring the
saturation temperature T.sub.50 of the refrigerant at the inlet of
the evaporator 13 either by means of an intrusive or direct
temperature probe 51, that is to say a probe directly bathed by the
refrigerant (FIG. 7), or by a nonintrusive or indirect probe 52,
which measures the temperature of the refrigerant on the basis of
the temperature of the tube that is transporting it (FIG. 8).
[0120] FIGS. 10 and 11 show the possibility of measuring the
saturation temperature T.sub.50 of the refrigerant at the outlet of
the evaporator 13 using means identical to the temperature
measurement envisaged at the inlet of the evaporator 13.
[0121] This method of determining the refrigerant pressure at the
inlet of the compressor is summarized in FIG. 13 in the form of a
block diagram in which: [0122] if the temperature T.sub.50 at the
inlet or at the outlet of the evaporator is estimated, then the
following are used: [0123] the evaporator efficiency .eta..sub.evap
determined from the information available about the vehicle, such
as blower voltage U and the run speed V of the vehicle, [0124]
these two items of information are used also to determine the
temperature T60 of the air to be cooled, combined with the
temperature inside the passenger compartment and the external
temperature and [0125] the evaporator efficiency .eta..sub.evap,
the temperature T.sub.60 of the air to be cooled and the surface
temperature T.sub.40 of the evaporator are combined to estimate the
temperature T.sub.50 at the inlet of the evaporator 13; [0126] if
the temperature T.sub.50 is measured, a temperature probe 51 or 52
delivers the expected value; [0127] the estimated or measured
temperature T.sub.50 is used to determine the pressure P.sub.50
according to the refrigerant saturation law; [0128] this pressure
P.sub.50 at the inlet or the outlet of the evaporator 13, combined
with the refrigerant pressure P.sub.20 at the inlet of the
expander, with the density .rho. of the CO.sub.2 refrigerant and
the flow area S (in mm.sup.2) of the expander allows the
refrigerant mass flow rate to be determined; and [0129] finally,
the combination of this mass flow rate information with the
estimate of the pressure P.sub.50 at the inlet of the evaporator
allows the refrigerant pressure P.sub.35 at the inlet of the
compressor to be determined without using a specific sensor and
thus without increasing the cost of the air conditioning unit.
[0130] FIG. 14 illustrates the relationship between the refrigerant
mass flow rate and the refrigerant pressure P.sub.35 at the inlet
of the compressor. The x-axis of this curve represents the mass
flow rate m.sub.exp in kilograms per hour and the y-axis of this
curve illustrates the pressure drop .DELTA.p in bar between the
inlet or the outlet of the evaporator 13 and the inlet of the
compressor 14. It may be seen that an error of around 30 kg in the
estimate of the mass flow rate results in an error of around 2 bar
in the determination of P.sub.35. This error is minor compared with
the absolute operating pressure values, which are often greater
than 35 bar.
[0131] The refrigerant temperature relative to the compressor may
be the refrigerant temperature T.sub.35 at the inlet of the
compressor, in accordance with equation A81 of Appendix A. R is the
perfect gas constant and M corresponds to the molar mass of the
refrigerant. The ratio R/M may especially be equal to 188.7.
[0132] As a variant, the refrigerant temperature relative to the
compressor may be the refrigerant temperature T.sub.36 at the
outlet of the compressor in accordance with equation A82 of
Appendix A.
[0133] FIG. 3 is a flow diagram showing the steps implemented by
the electronic card for estimating the refrigerant mass flow rate
m.sub.exp and the power consumed by the compressor.
[0134] At step 100, the refrigerant pressure P.sub.20 at the inlet
of the expander is estimated/measured. Referring to FIGS. 1B, 6 and
7, the refrigerant pressure P.sub.20 at the inlet of the expander
may be measured by a sensor 20 placed at the inlet of the expander.
As a variant, the pressure P.sub.20 of the refrigerant at the inlet
of the expander may be estimated.
[0135] At step 102, the electronic card 401 estimates the flow area
S of the expander 12 from the measured/estimated refrigerant
pressure value P.sub.20 at the inlet of the expander in accordance
with equations A4 and A5 of Appendix A.
[0136] Step 102 is shown in detail in the flow diagram of FIG. 4.
The electronic card determines if the measured value of the
refrigerant pressure P.sub.20 at the inlet of the expander is:
[0137] less than or equal to the first pressure value P1 (step
1020), in which case the flow area of the expander is equal to S1;
[0138] greater than the first constant P1 and less than or equal to
the second pressure value P2 (step 1021), in which case the flow
area of the expander is given by equation A3 of Appendix A as a
function of the pressure P.sub.20 obtained at step 100; [0139]
greater than the second pressure value P2 and less than or equal to
the third pressure value P3 (step 1022), in which case the flow
area of the expander is given by equation A4 of Appendix A, as a
function of the pressure P.sub.20 obtained at step 100; and [0140]
greater than or equal to the third pressure value P3 (step 1023),
in which case the flow area of the expander is equal to S4.
[0141] At step 103, the electronic card provides an
estimate/measurement of the temperature T.sub.30 at the inlet of
the expander. The unit may include a temperature sensor 30 for
measuring the refrigerant temperature T.sub.30 at the inlet of the
expander, as shown in FIGS. 1B, 6 and 7. As a variant, the unit may
include a single sensor 20 for measuring both the pressure P.sub.20
and the temperature T.sub.30 of the refrigerant at the inlet of the
expander. The refrigerant temperature T.sub.30 at the inlet of the
expander may also be estimated.
[0142] At step 104, the electronic card 401 estimates the density
.rho. of the CO.sub.2 refrigerant. The density .rho. of the
CO.sub.2 refrigerant may be calculated according to equation A11 of
Appendix A from the refrigerant pressure P.sub.20 at the inlet of
the expander, obtained at step 100, and from the refrigerant
temperature T.sub.30 at the inlet of the expander, obtained at step
103.
[0143] At step 105 of FIG. 3, the electronic card 401 can then
calculate the refrigerant mass flow rate m.sub.exp according to
equation A3 of Appendix A, from: [0144] the refrigerant pressure
P.sub.20 at the inlet of the expander, estimated/measured at step
100; [0145] the flow area S (in mm.sup.2) of the expander,
estimated at step 102; and [0146] the density .rho. of the CO.sub.2
refrigerant, estimated at step 104.
[0147] As a complement, the estimate of the refrigerant mass flow
rate m.sub.exp at the expander may be used to calculate the power
P.sub.abs consumed by the compressor.
[0148] FIG. 5 is a flow diagram showing the steps implemented by
the electronic card for calculating the power P.sub.abs consumed by
the compressor from the estimate of the refrigerant mass flow rate
m.sub.exp at the expander. The estimate of the power absorbed by
the compressor may in particular require a prior estimate of the
work .DELTA.H.sub.ise of the compressor, in accordance with
equations A6 and A7 of Appendix A.
[0149] At step 200, the electronic card calculates an estimate of
the work .DELTA.H.sub.ise of the compressor in accordance with
equation A8 of Appendix A from: [0150] the refrigerant pressure
P.sub.20 at the inlet of the expander; [0151] the refrigerant
pressure P.sub.35 at the inlet of the compressor; and [0152] the
refrigerant temperature T.sub.comp relative to the compressor.
[0153] When the refrigerant temperature relative to the compressor
is the refrigerant temperature T.sub.35 at the inlet of the
compressor (in accordance with equation A81 of Appendix A), it can
be measured by a probe 35 placed at the inlet of the compressor, as
shown in FIGS. 1B and 6.
[0154] When the refrigerant temperature relative to the compressor
is the refrigerant temperature T.sub.36 at the outlet of the
compressor (in accordance with equation A82 of Appendix A), it can
be measured by a probe 36 placed at the outlet of the compressor,
as shown in FIG. 7.
[0155] The refrigerant pressure P.sub.12 at the inlet of the
compressor may be estimated or measured.
[0156] At step 202, the electronic card calculates the isentropic
power W.sub.ise from the refrigerant mass flow rate m.sub.exp
obtained at step 105 and the work .DELTA.H.sub.ise of the
compressor obtained at step 200, in accordance with equation A7 of
Appendix A.
[0157] At step 204, the electronic card calculates an estimate of
the power P.sub.abs absorbed by the compressor, according to
equation A6 of Appendix A, from the isentropic power W.sub.ise
obtained at step 202 and the rotation speed N of the
compressor.
[0158] The rotation speed N of the compressor is supplied to the
electronic card by the engine fuel injection computer 42 via the
link 33, with reference to FIG. 1B.
[0159] The computer may use the estimated value of the actual power
consumed by the compressor to adjust the injection parameters,
thereby making it possible to reduce the fuel consumption.
[0160] The air conditioning unit according to the invention makes
it possible to obtain a satisfactory estimate of the refrigerant
mass flow rate at the expander. Furthermore, this unit does not use
a low-pressure sensor to estimate the refrigerant mass flow rate at
the expander, thereby allowing the total cost of the unit to be
reduced.
[0161] Of course, the present invention is not limited to the
embodiments described above. It encompasses all alternative
embodiments that a person skilled in the art might envision.
[0162] The present invention also covers the software code that it
uses, most particularly when this is available on any medium that
can be read by a computer. The expression "medium that can be read
by a computer" covers a storage medium, for example a magnetic or
optical storage medium, and also a transmission means, such as a
digital or analog signal.
APPENDIX A
[0163] Supercritical Refrigerant Mass Flow Rate m.sub.exp=KS.rho.
ln(P.sub.20+C) (A10) .rho.=f(T.sub.30, P.sub.20) (A11)
[0164] Flow Area S of the Expander
[0165] IF P.sub.20.ltoreq.P1: S=S1 (A2)
[0166] If P1<P.sub.20.ltoreq.P2:
S=S1+(S2-S1)(P.sub.20-P1)/(P2-P1) (A3)
[0167] If P2<P.sub.20.ltoreq.P3:
S=S2+(S3-S2)/(P.sub.20-P2)/(P3-P2) (A4)
[0168] If P.sub.20.gtoreq.P3: S=S4 (A5)
[0169] Power Consumed by the Compressor P.sub.abs=aW.sub.ise+bN
(A6)
[0170] Isentropic Power W.sub.ise
W.sub.ise=m.sub.exp.DELTA.H.sub.ise (A7)
[0171] Work .DELTA.H.sub.ise of the Compressor
.DELTA.H.sub.ise=f(P.sub.20, P.sub.35, T.sub.35) (A80)
.DELTA.H.sub.ise=[(P.sub.20/P.sub.35).sup.(k-1)/k-1](T.sub.35+273.15)(R/M-
)/(k-1) (A81)
.DELTA.H.sub.ise=[1-(P.sub.20/P.sub.35).sup.(1-k)/k](T.sub.36+273.15)(R/M-
)/(k-1) (A82)
[0172] Estimate of the Refrigerant Pressure P.sub.35 at the Inlet
of the Compressor .DELTA.p=P.sub.50-P.sub.35 (A90) .DELTA.p=k
.rho.vCo.sub.2/2 (A100) Vco.sub.2=M.sub.exp/(.rho.S) (A101)
P.sub.36=P.sub.50-M.sub.expK(2.rho.S.sup.2) (A9)
T.sub.60=(T.sub.40-(1-.eta..sub.evap)T.sub.60)/.eta..sub.evap (A91)
T.sub.50=>P.sub.60 R744 refrigerant saturation law
* * * * *