U.S. patent application number 10/287917 was filed with the patent office on 2003-06-12 for variable displacement type compressor, air conditioner with the variable displacement type compressor, and method for controlling displacement in the variable displacement type compressor.
Invention is credited to Kawaguchi, Masahiro, Koumura, Satoshi, Ota, Masaki, Tarutani, Tomoji, Umemura, Satoshi.
Application Number | 20030108432 10/287917 |
Document ID | / |
Family ID | 19154946 |
Filed Date | 2003-06-12 |
United States Patent
Application |
20030108432 |
Kind Code |
A1 |
Kawaguchi, Masahiro ; et
al. |
June 12, 2003 |
Variable displacement type compressor, air conditioner with the
variable displacement type compressor, and method for controlling
displacement in the variable displacement type compressor
Abstract
A variable displacement type compressor circulates a fluid in an
air conditioning circuit. The compressor has a compression
mechanism and a displacement control valve. The compression
mechanism compresses the fluid. The displacement control valve
controls discharge amount of the fluid of the compressor. In a
first predetermined range of discharge pressure, suction pressure
decreases at a first variation as the discharge pressure increases.
In a second predetermined range of the discharge pressure that is
higher than the first predetermined range, the suction pressure
varies at a second variation as the discharge pressure increases.
The second variation is constituted of at least one of a third
variation that is smaller than the first variation and at which the
suction pressure decreases as the discharge pressure increases, a
fourth variation at which the suction pressure increases as the
discharge pressure increases, and substantially zero.
Inventors: |
Kawaguchi, Masahiro;
(Kariya-shi, JP) ; Umemura, Satoshi; (Kariya-shi,
JP) ; Koumura, Satoshi; (Kariya-shi, JP) ;
Ota, Masaki; (Kariya-shi, JP) ; Tarutani, Tomoji;
(Kariya-shi, JP) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
345 Park Avenue
New York
NY
10154
US
|
Family ID: |
19154946 |
Appl. No.: |
10/287917 |
Filed: |
November 5, 2002 |
Current U.S.
Class: |
417/222.2 |
Current CPC
Class: |
F04B 27/1804
20130101 |
Class at
Publication: |
417/222.2 |
International
Class: |
F04B 001/26 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 6, 2001 |
JP |
P2001-340800 |
Claims
What is claimed is:
1. A variable displacement type compressor that circulates a fluid
in an air conditioning circuit, the fluid being drawn into a
suction region before compression, the pressure in the suction
region being defined as suction pressure, tho fluid being
discharged to tho discharge region after compression, the pressure
in the discharge region being defined as discharge pressure, the
suction region being connected to the discharge region, the
compressor comprising: a compression mechanism for compressing the
fluid; and a displacement control valve for controlling discharge
amount of the fluid of the compressor, in a first predetermined
range of the discharge pressure the suction pressure decreasing at
a first variation as the discharge pressure increases, in a second
predetermined range of the discharge pressure that is higher than
the first predetermined range the suction pressure varying at a
second variation as the discharge pressure increases, the second
variation being constituted of at least one of a third variation
that is smaller than the first variation and at which the suction
pressure decreases as the discharge pressure increases, a fourth
variation at which the suction pressure increases as the discharge
pressure increases, and substantially zero.
2. The variable displacement type compressor according to claim 1,
wherein the suction pressure increases or is maintained to a
predetermined value as the discharge pressure increases in the
second predetermined range.
3. The variable displacement type compressor according to claim 1,
wherein the suction pressure increases as the discharge pressure
increases in a third predetermined range of the discharge pressure
that is lower than the first predetermined range.
4. The variable displacement type compressor according to claim 3,
wherein the discharge amount is controlled by introducing the
compressed fluid from the discharge region to a crank chamber
pressure region, the displacement control valve further comprising:
a communication route communicating the discharge region and the
crank chamber pressure region; a valve body for opening and closing
the communication route by sensing the suction pressure and the
discharge pressure; and an urging means for enabling to urge the
valve body so as to open or close the communication route, the
urging means urging the valve body so as to open the communication
route in the second predetermined range.
5. The variable displacement type compressor according to claim 4
wherein the urging means urges the valve body so as to close the
communication route in the third predetermined range.
6. The variable displacement type compressor according to claim 5,
the urging means further comprising: a rod for contacting the valve
body in the third predetermined range; a rod supplementing member
for urging the valve body so as to open the communication route in
the second predetermined range; and a spring for applying elastic
urging force to the rod and the rod supplementing member, the rod
and the rod supplementing member being operated based on a balance
between the discharge pressure of the fluid and the elastic urging
force of the spring.
7. The variable displacement type compressor according to claim 3,
wherein the suction pressure and the discharge pressure have a
first inflectional point that connects the third predetermined
range to the second predetermined range.
8. The variable displacement type compressor according to claim 1,
wherein the suction pressure and the discharge pressure have a
second inflectional point that connects the first predetermined
range to the second predetermined range.
9. An air conditioner comprising: an air conditioning circuit
including a fluid; a condenser in the air conditioning circuit for
condensing the fluid; an expansion valve in the air conditioning
circuit for expanding the condensed fluid; an evaporator in the air
conditioning circuit for evaporating the expanded fluid to exchange
heat between the fluid and air in a room; and a variable
displacement type compressor in the air conditioning circuit for
compressing the evaporated fluid, the fluid being drawn into a
suction region before compression, the pressure in the suction
region being defined as suction pressure, the fluid being
discharged to the discharge region after compression, the pressure
in the discharge region being defined as discharge pressure, the
suction region being connected to the discharge region, the
compressor comprising; a compression mechanism for compressing the
fluid; and a displacement control valve for controlling discharge
amount of the fluid of the compressor, in a first predetermined
range of the discharge pressure the suction pressure decreasing at
a first variation as the discharge pressure increases, in a second
predetermined range of the discharge pressure that is higher than
the first predetermined range the suction pressure varying at a
second variation as the discharge pressure increases, the second
variation being constituted of at least one of a third variation
that is smaller than the first variation and at which the suction
pressure decreases as the discharge pressure increases, a fourth
variation at which the suction pressure increases as the discharge
pressure increases, and substantially zero.
10. A method for controlling displacement in a variable
displacement type compressor that circulates a fluid in an air
conditioning circuit, the fluid being drawn into a suction region
before compression, the pressure in the suction region being
defined as suction pressure, the fluid being discharged to the
discharge region after compression, the pressure in the discharge
region being defined as discharge pressure, the suction region
being connected to the discharge region, the method comprising the
steps of: decreasing the suction pressure at a first variation as
the discharge pressure increases in a first predetermined range of
the discharge pressure; setting a third variation that is smaller
than the first variation and at which the suction pressure decrease
as the discharge pressure increases in a second predetermined range
of the discharge pressure that is higher than the first
predetermined range; setting a fourth variation at which the
suction pressure increases as the discharge pressure increases in
the second predetermined range; setting a second variation by using
at least one of the third variation, the fourth variation, and
substantially zero in the second predetermined range; and varying
the suction pressure at the second variation as the discharge
pressure increases in the second predetermined range.
11. The method for controlling displacement in the variable
displacement type compressor according to claim 10, wherein the
second variation setting step comprises increasing tho suction
pressure or maintaining to a predetermined value as the discharge
pressure increases.
12. The method for controlling displacement in the variable
displacement type compressor according to claim 11, comprising the
additional step of increasing the suction pressure as the discharge
pressure increases in a third predetermined range of the discharge
pressure that is lower than the first predetermined range.
13. The method for controlling displacement in the variable
displacement type compressor according to claim 12, comprising the
additional step of providing the suction pressure and the discharge
pressure with a first inflectional point that connects the third
predetermined range to the second predetermined range.
14. The method for controlling displacement in the variable
displacement type compressor according to claim 10, comprising the
additional step of providing the suction pressure and the discharge
pressure with a second inflectional point that connects the first
predetermined range to the second predetermined range.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to a variable
displacement type compressor adapted for use in an air conditioner,
and more specifically to a displacement control system for the
variable displacement type compressor which makes it possible to
achieve the desired air conditioning performance by appropriately
controlling the displacement of the compressor.
[0002] A variable displacement type compressor, for example, for
use in an automotive air conditioner has incorporated therein a
control valve for controlling discharge amount of a refrigerant. In
the compressor equipped with such a control valve, operating
performance of the air conditioner varies depending on the
relationship between the discharge pressure and suction pressure of
the refrigerant. FIG. 12 shows three different operating regions A,
B and C of the compressor, indicated by shaded areas, in connection
with the relationship between the discharge pressure Pd and suction
pressure Ps of the refrigerant. The region A represents a region
where the compressor is operating under a low cooling load and with
low discharge pressure Pd. In such an operating state, a mist tends
to be formed on the interior surface of vehicle windshield with an
increase in the suction pressure Ps and hence the refrigerant
pressure at the outlet of an evaporator connected in the air
conditioning system, thus offering a problem of insufficient
de-misting performance of the air conditioner. In the region B
where the compressor is operating similarly under a low cooling
load and with a low discharge pressure Pd, the evaporator tends to
be frosted with a decrease in the suction pressure Ps. In the
region C where the compressor is in operation under a high cooling
load and with high discharge pressure, cooling performance of the
air conditioner tends to be reduced with an increase in the suction
pressure Ps. Thus, there has been a demand for a control system of
an air conditioner which is designed in view of the above
problems.
[0003] Various displacement control valves for an air conditioning
system are disclosed in Japanese Unexamined Patent Publications No.
4-321779. No. 6-123279 and No. 7-119642, which are designed to
achieve the desired air conditioning performance by appropriately
controlling the displacement of a variable displacement type
compressor. A compressor using such displacement control valve can
prevent the aforementioned problems by achieving Pd-Ps
characteristic as represented by a curve in FIG. 12.
[0004] According to the Pd-Ps characteristic curve of FIG. 12,
however, the suction pressure is decreased excessively in the
control region of high cooling loads ant the compressor is operated
continuously, with the result that the engine for driving the
compressor is applied with an excessive load and the coolant in a
radiator of the engine is heated accordingly.
SUMMARY OF THE INVENTION
[0005] The present invention relates to a variable displacement
type compressor, an air conditioning system equipped with such a
compressor and a method for controlling the displacement of such a
compressor which will not impose an excessive load on an engine
while the compressor is running under a high load.
[0006] According to the present invention, a variable displacement
type compressor circulates a fluid in an air conditioning circuit.
The fluid is drawn into a suction region before compression. The
pressure in the suction region is defined as suction pressure. The
fluid is discharged to the discharge region after compression. The
pressure in the discharge region is defined as discharge pressure.
The suction region is connected to the discharge region. The
compressor has a compression mechanism and a displacement control
valve. The compression mechanism compresses the fluid. The
displacement control valve controls discharge amount of the fluid
of the compressor. In a first predetermined range of the discharge
pressure the suction pressure decreases at a first variation as the
discharge pressure increases. In a second predetermined range of
the discharge pressure that is higher than the first predetermined
range the suction pressure varies at a second variation as the
discharge pressure increases. The second variation is constituted
of at least one of a third variation that is smaller than the first
variation and at which the suction pressure decreases as the
discharge pressure increases, a fourth variation at which the
suction pressure increases as the discharge pressure increases, and
substantially zero.
[0007] The present invention also provides a method for controlling
displacement in a variable displacement type compressor that
circulates a fluid in an air conditioning circuit. The fluid is
drawn into a suction region before compression. The pressure in the
suction region is defined as suction pressure. The fluid is
discharged to the discharge region after compression. The pressure
in the discharge region is defined as discharge pressure. The
suction region is connected to the discharge region. The method
comprises the steps of decreasing the suction pressure at a first
variation as the discharge pressure increases in a first
predetermined range of the discharge pressure, setting a third
variation that is smaller than the first variation and at which the
suction pressure decrease as the discharge pressure increases in a
second predetermined range of the discharge pressure that is higher
than the first predetermined range, setting a fourth variation at
which the suction pressure increases as the discharge pressure
increases in the second predetermined range, setting a second
variation by using at least one of the third variation, the fourth
variation, and substantially zero in the second predetermined
range, and varying the suction pressure at the second variation as
the discharge pressure increases in the second predetermined
range.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The features of the present invention that are believed to
be novel are set forth with particularity in the appended claims.
The invention together with objects and advantages thereof, may
best be understood by reference to the following description of the
presently preferred embodiments together with the accompanying
drawings in which:
[0009] FIG. 1 is a longitudinal sectional view illustrating a
variable displacement swash plate type compressor 100 according to
a preferred embodiment of the present invention;
[0010] FIG. 2 is an enlarged longitudinal sectional view
illustrating a displacement control valve 30, which is shown in
FIG. 1, under a low-load control range R3 according to the
preferred embodiment of the present invention;
[0011] FIG. 3 is an enlarged perspective view illustrating a valve
box 60, a valve body 40 and a partial discharge pressure correction
rod 41 in FIG. 2 according to the preferred embodiment of the
present invention;
[0012] FIG. 4 is an enlarged longitudinal sectional view
illustrating a displacement control valve 30, which is shown in
FIG. 1, under an intermediate-load control range R1 according to
the preferred embodiment of the present invention;
[0013] FIG. 5 is an enlarged longitudinal sectional view
illustrating a displacement control valve 30, which is shown in
FIG. 1, under a high-load control range R2 according to the
preferred embodiment of the present invention;
[0014] FIG. 6 is a graph illustrating a Pd-Ps characteristic curve
when the displacement control valve 30 according to the preferred
embodiment of the present invention is used;
[0015] FIG. 7 is a schematic view illustrating various forces
acting in the displacement control valve 30 during compressor
operation in the low-load control range R3 according to the
preferred embodiment of the present invention;
[0016] FIG. 8 is a schematic view illustrating various forces
acting in the displacement control valve 30 during compressor
operation in the intermediate-load control range R1 according to
the preferred embodiment of the present invention;
[0017] FIG. 9 is a schematic view illustrating various forces
acting in the displacement control valve 30 during compressor
operation in the high-load control range R2 according to the
preferred embodiment of the present invention;
[0018] FIG. 10 is a longitudinal sectional view illustrating a
displacement control valve 130 according to another preferred
embodiment of the present invention;
[0019] FIG. 11 is a cross sectional view illustrating a spring 80,
spring washers 81 and 82, a through hole 82a, a valve body 40 and a
partial discharge pressure correction rod according to yet another
preferred embodiment of the present invention; and
[0020] FIG. 12 is a graph illustrating a Pd-Ps characteristic curve
when a displacement control valve according to a prior art is
used.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0021] The following will describe a preferred embodiment of a
variable displacement type compressor according to the present
invention while having reference to the accompanying drawings. It
is noted the following description will deal with a variable
displacement swash plate type compressor adapted for use in an
automotive air conditioning system.
[0022] Referring firstly to FIG. 1, the variable displacement swash
plate type compressor 100 (referred to merely as "compressor"
hereinafter) includes a cylinder block 1 having formed therein a
plurality of cylinder bores 1a arranged around the central axis of
the cylinder block 1 and each receiving therein a reciprocally
movable piston 18. A front housing 2 is sealingly fastened to the
front end of the cylinder block 1, and a rear housing 5 is
similarly fastened to the rear end of the cylinder block 1 with a
valve plate assembly 6 interposed therebetween. The cylinder block
1 and the front housing 2 cooperate to define a crank chamber 9 as
a crank chamber pressure region in which a wobble plate 15 and its
associated parts are disposed as will be described in detail in
later part hereof.
[0023] The rear housing 5 has formed therein a suction chamber 3 as
a suction region or a suction pressure region into which
refrigerant before compression is drawn and a discharge chamber 4
as a discharge region or a discharge pressure region into which
refrigerant compressed in tho respective cylinder bores 1a is
discharged. The valve plate assembly 6 is formed therethrough with
a suction port for providing communication between the suction
chamber 3 and each cylinder bore 1a through a suction valve 3a and
also with a discharge port for communication between the discharge
chamber 4 and each cylinder bore 1a through a discharge valve 4a. A
retainer 4b is fixed in the discharge chamber 4 so as to limit the
maximum opening of the discharge valve 4a. On the rear side of the
rear housing 5 is provided a displacement control valve 30 serving
as the displacement control means of the present invention which
will be described in detail in later part hereof.
[0024] A first supply passage 20 extends through the cylinder block
1 and the rear housing 5 for communication between the crank
chamber 9 and the displacement control valve 30. A bleed passage 21
having therein an orifice 21a is formed in the cylinder block 1 for
communication between the crank chamber 9 and the suction chamber
3. Furthermore, the rear housing 5 has formed therein a pressure
sensing passage 22 and a second supply passage 23 for communication
of the suction chamber 3 and the discharge chamber 4 with the
displacement control valve 30, respectively, as will be described
more in detail with reference to FIG. 2.
[0025] As shown in FIG. 1, a drive shaft 8 is disposed in the crank
chamber 9 and rotatably supported in the cylinder block 1 and the
front housing 2 by bearings 1b and 2b arranged in the cylinder
block 1 and the front housing 2, respectively. The drive shaft 8 is
connected at the front end thereof to a vehicle engine by way of a
suitable clutching means such as electromagnetic clutch (not
shown). A shaft seal 2a is provided between the drive shaft 8 and
the front housing 2. It is noted that the compressor 100 may
dispense with the clutch so that the drive shaft 8 is driven
constantly by means of a belt and pulley arrangement.
[0026] A rotor 7 is fixedly mounted on the drive shaft 8 for
rotation therewith in the crank chamber 9 with a thrust bearing 2c
disposed between the rotor 7 and the inner wall of the front
housing 2, and a sleeve 19 is axially slidably mounted on the drive
shaft 8 adjacent to the rotor 7. The rotor 7 is formed with an
elongated through-hole 7b through which a pin 11a of a swash plate
11 is inserted slidably in the elongated through-hole 7b. The swash
plate 11 is rotatable with the drive shaft 8 and pivotally
supported by a pair of trunnion pins 19a projecting from opposite
sides of the sleeve 19 so that, as the drive shaft 8 is rotated,
the swash plate 11 makes a nutational motion about the drive shaft
8 at an inclination angle. A wobble plate 15 is fitted to the swash
plate 11 by way of a thrust bearing 12, a plane bearing 10, a race
13 and a thrust washer 14, and a guide rod 16 extends in the crank
chamber 9 to prohibit rotation of the wobble plate 15. Each of the
pistons 18 received in the cylinder bores 1a is connected to the
wobble plate 15 by a rod 17. In operation, the wobble plate 15
makes a wobbling movement in response to the nutational motion of
the swash plate 11 and the pistons 18 connected to the wobble plate
15 are caused to move reciprocally in their associated cylinder
bores 1a. Refrigerant is drawn from the suction chamber 3 into the
cylinder bore 1a during the suction stroke of the piston 18 and
then compressed in and then discharged out of the cylinder bore 1a
during the discharge stroke of the piston 18, thus compressed
refrigerant being discharged into the discharge chamber 4.
[0027] Displacement of the compressor 100 depends on the length of
stroke of the piston 18 and such stroke length varies with the
inclination angle of the swash plate 11. To be more specific, the
stroke length of the piston 18 and hence the displacement is
increased with an increase of the angle at which the swash plate 11
is inclined with respect to a plane perpendicular to the axis of
the drive shaft 8, and vice versa. This inclination angle of the
swash plate 11 during compressor operation is determined by the
pressure differential between the pressure in the cylinder bores 1a
and in the crank chamber 9, and this pressure differential is
adjusted by the displacement control valve 30.
[0028] The following will describe the structure of the
displacement control valve 30 while having reference to FIGS. 2 and
3.
[0029] Referring to firstly FIG. 2, the displacement control valve
30 includes a main valve portion 33, a cylindrical housing 31 fixed
at one end thereof to one end of the main valve portion 33, and a
cap 38 fixed to the other end of the main valve portion 33. An
adjusting portion 32 is screwed into the other end of the
cylindrical housing 31 by way of an O-ring, and an insert 37 is
disposed in the cap 38.
[0030] The main valve portion 33, the cylindrical housing 31 and
the adjusting portion 32 cooperate to define a suction pressure
chamber 51 as a suction region which is in communication with the
suction chamber 5 via the aforementioned pressure sensing passage
22 in the rear housing 5 and radial passages 51 a formed in the
cylindrical housing 31. Thus, suction pressure Ps prevails in the
suction pressure chamber 51 of the displacement control valve 30.
Within the suction pressure chamber 51 is disposed a bellows 36
having one end thereof fixed to the adjusting portion 32 and the
other end thereof engaged with a rod 35 which is slidably disposed
in an axial bore formed in the main valve portion 33. The bellows
36 has therein a spring 30a urging the bellows 36 in the direction
indicated by arrow F.sub.1 and the bellows interior is maintained
under vacuum. F.sub.1 represents the sum of the elastic force of
the bellows 36 and the urging force of the spring 36a both acting
in the same arrow direction. The bellows 36, which serves as the
suction pressure Ps sensitive means of the invention, has an
effective pressure sensing area S1 to which suction pressure Ps
acts in the direction opposite to the arrow direction F.sub.1. It
is noted that any suitable means such as diaphragm may be used in
place of the bellows 36 an the suction pressure Ps sensitive means
of the invention.
[0031] The rod 35 is slidable in the axial bore in the main valve
portion 33 by contraction or expansion of the bellows 36. The main
valve portion 33 has formed therein at an intermediate position
thereof an axial bore 20b into which the distal end of the rod 35
extends and first radial supply ports 20a extending radially from
the axial bore 20b. The first supply ports 20a are in communication
with the aforementioned first supply passage 20 formed through the
cylinder block 1 and the rear housing 5 for communication with the
crank chamber 9. The axial bore 20b is formed with a cross
sectional area S2.
[0032] The main valve portion 33 and the insert 37 define
therebetween a discharge pressure chamber 52 as a discharge region
which is in communication with the discharge chamber 4 through the
second supply passage 23 formed in the rear housing 5 and second
radial supply ports 23a which are formed in the main valve portion
33. The first supply passage 20, the first supply port 20a, the
second supply passage 23 and the second supply port 23a constitute
communication routes of the variable displacement type compressor
according to the present invention.
[0033] The insert 37 and the cap 38 have defined therebetween a
crank pressure chamber 53 as a crank chamber pressure region which
is in communication with the crank chamber 9 of the compressor 100
by way of a communication passage 33a formed in the main valve
portion 33.
[0034] The insert 37 is formed at the axial center thereof with an
axial bore through which a discharge pressure correction rod 41,
which serves as the discharge pressure sensitive means of the
invention, is slidably inserted. This rod 41 has a flange portion
41a disposed in the discharge pressure chamber 52 and a stem
portion 41b passing through the insert 37 and extending into the
crank pressure chamber 53. A spring 12 having a spring constant
k.sub.2 is provided in the crank pressure chamber 53 for urging the
correction rod 11 toward the discharge pressure chamber 52 as
indicated by arrow 70 with force F.sub.2. The stem portion 41b of
the correction rod 41 has a cross sectional area S3.
[0035] As shown in FIGS. 2 and 3, a valve box 60 serving as the rod
supplementing member of the invention is disposed within the
discharge pressure chamber 52, and a valve body 40 in the form of a
spherical ball serving as the valve means of the invention and part
of the correction rod 41 including its flange portion 41a and part
of the stem portion 41b adjacent to the flange portion 41a are
incorporated within the valve box 60. A spring 63 with a spring
constant k.sub.3 is disposed between the flange portion 41a and the
inner end of the valve box 60. Part of the valve body 40 which
protrudes out of the valve box 60 through its first opening 61 is
contactable with the rod 35. The discharge pressure correction rod
41 is movable axially through the opposite second opening 62 of the
valve box 60. The discharge pressure correction rod 41, the spring
42 and the valve box 60 constitute the urging means of the present
invention. Reference numeral 39 designates a valve seat for the
valve body 40.
[0036] It is noted that the cross sectional areas of S1, S2 and S3
of the bellows 36, the axial bore 20b and the stem portion 41b of
the correction rod 41, respectively, are provided such that
S1>S3>S2.
[0037] The compressor 100 having incorporated therein such
displacement control valve 30 is disposed in a refrigeration
circuit together with a condenser, expansion valve, evaporator,
etc. (not shown). When the drive shaft 8 is driven to rotate by
vehicle engine, the swash plate 11 is rotated at an inclined angle
by the rotor 7 that is fixed on and hence rotatable with the drive
shaft 8. The wobble plate 15 fitted to the swash plate 11 makes a
wobbling movement at the inclined angle of the swash plate 11,
which causes the pistons 18 to move reciprocally in their
associated cylinder bores 1a for a stroke length corresponding to
the inclined angle of the wobble plate 15. In so doing, refrigerant
flowing from the evaporator to the suction chamber 3 is drawn into
the cylinder bore 1a then in suction stroke. Refrigerant introduced
in the cylinder bore 1a is compressed by the piston 18 and then
discharged into the discharge chamber 4.
[0038] As is apparent from the foregoing description, the
displacement control valve 30 is provided as an internal control
mechanism of the compressor 100 wherein the valve body 40 of the
displacement control valve 30 is operable by way of the bellows 36
as the suction pressure sensitive means and the discharge pressure
correction rod 41 as the discharge pressure sensitive means,
respectively.
[0039] The displacement control valve 30 thus constructed is
configured such that a Pd-Ps characteristic curve as indicated by a
solid line in FIG. 6 is achieved, as compared with a curve of a
dotted line achievable by prior art.
[0040] Referring now specifically to FIG. 6 showing two Pd-Ps
characteristic curves, wherein the solid line curve shows Pd-Ps
characteristic achievable by use of the displacement control valve
30 of the illustrated embodiment, while the dotted line curve
represents similar characteristic of the prior art control valves.
In the diagram of FIG. 6, symbols T1 and T2 depict infection points
of Pd-Ps characteristic curve of the displacement control valve 30,
so that the curve may be divided into three line sections L1, L2
and L3 by such inflection points T1 and T2.
[0041] The displacement control valve 30 is configured to operate
as follows. In the low-load control region R3 (or the third mode in
the invention) corresponding to the line section L3 where the
compressor 100 is operating under a low discharge pressure Pd and
hence with a low displacement, suction pressure Ps increases with
an increase in discharge pressure Pd. In the intermediate-load
control range R1 (or the first mode in the invention) corresponding
to the line section L1 between the inflection points T1 and T2
where discharge pressure Pd is in a middle range, the suction
pressure Ps decreases with an increase of discharge pressure Pd. In
the high-load control range R2 corresponding to the line section L2
(or the second mode in the invention) where the compressor 100 is
operating under a high discharge pressure Pd and hence with a high
displacement, suction pressure Ps is maintained substantially at a
constant level irrespective of a change of discharge pressure Pd.
In the control range R2, suction pressure Ps is prevented from
being dropped.
[0042] As shown in FIG. 6, the Pd-Ps characteristic describes a
curve so that it avoids interference with any of the shaded region
A where a mist tends to be produced, the region B where evaporator
frosting tends to occur and the region C where cooling performance
tends to be decreased. In other words, the compressor 100 operating
according the Pd-Ps characteristic curve can forestall these three
problems.
[0043] As appreciated from FIG. 6, suction pressure Ps in the
intermediate-load control range R1 between the inflection points T1
and T2 is generally raised or set higher than that of the
characteristic curve attainable by the prior art control valves as
indicated by a dotted line, without interfering with the operating
region C. Furthermore, suction pressure Ps in the high-load control
range R2 of the Pd-Ps characteristic curve is maintained
substantially while avoiding interference with the operating region
C. As is apparent from comparison with the dotted line, maintenance
of a substantially constant suction pressure Ps in the high-load
control range R2 is accomplished by providing the inflection point
T2 between the line sections L1 and L2 so as to differentiate the
inclinations of the line sections L1 and L2.
[0044] According to the Pd-Ps characteristic curve of the
displacement control valve 30 wherein suction pressure Ps is set
higher than heretofore in the intermediate-load control range R1,
fuel consumption can be improved. Additionally, suppressing a
decrease of suction pressure Ps in the high-load control range R2
helps not only to improve the fuel consumption but also to prevent
temperature rise of coolant in a vehicle radiator.
[0045] The following will describe the operation of the
displacement control valve 30 in the control ranges R3, R1 and R2
with reference to FIGS. 2, 4, 5 and 6.
[0046] FIG. 2 shows a state of the displacement control valve 30
when the compressor 100 is operating under a low load in the
control range R3. The discharge pressure correction rod 41 is urged
in the direction of the arrow 70 by the spring 42, and the valve
body 40 is pushed by the correction rod 41 accordingly to be seated
on the valve seat 39, so that the axial bore 20b which is in
communication with the crank chamber 9 through the first supply
passage 20 in the cylinder block 1 is shut off from the discharge
pressure chamber 52. That is, the discharge chamber 4 and the crank
chamber 9 are shut off from each other. In this state of FIG. 2,
the spring 63 has one end thereof free from contact with its
adjacent inner surface of the valve box 60 and hence provides no
urging action. Because the crank chamber 9 and the suction chamber
3 are in communication with each other by way of the bleed passage
21 having therein the orifice 21a, part of the refrigerant in the
crank chamber 9 flows into the suction chamber 3. Since flowing of
refrigerant under high pressure from the discharge chamber 4 into
the crank chamber 9 is shut off, crank chamber pressure Pc is
reduced and the back pressure acting on the pistons 18 is reduced,
accordingly. Therefore, the inclination angle of the wobble plate
15 is increased thereby to increase the stroke length of the
pistons 18, with the result that the displacement is increased. In
this state of the displacement control valve 30, the valve body 40
is not lifted off from the valve seat 39 unless suction pressure Ps
in the suction pressure chamber 51 is substantially reduced
relatively to the force F.sub.1. Therefore, suction pressure Ps is
increased with a build-up of discharge pressure Pd. At this state,
the crank chamber pressure Pc and the suction pressure Ps are
maintained substantially to be equal to each other.
[0047] From the schematic diagram of FIG. 7 showing various forces
acting in the displacement control valve 30 during compressor
operation in the low-load control range R3, the equilibrium state
of such forces can be expressed by equation (1), and transforming
this equation (1), the relationship between suction pressure Ps and
discharge pressure Pd can be expressed by equation (2), as
follows.
F1-S1.multidot.Ps+S2.multidot.Ps-S2.multidot.Pd+S3.multidot.Pd-S3.multidot-
.Ps-F2=0 (1)
Ps=-[(S2-S3)/(S1-S2+S3)].multidot.Pd+(F1-F2)/(S1-S2+S3) (2)
[0048] Expressing the equation (2) in a coordinate system with
discharge pressure Pd and suction pressure Ps represented by
abscissa and ordinate, respectively, as shown in FIG. 6, the
inclination of the line is determined by -(S2-S3)/(S1-S2+S3). Since
the cross-sectional areas of S1, S2 and S3 are such that
S1>S3>S2, the inclination of the line, or the manner in which
suction pressure Ps varies with discharge pressure in the Pd-Ps
characteristic line, is positive. That is, the displacement control
valve 30 provides Pd-Ps characteristic as shown by the line section
L3 of FIG. 6 in the low-load control range R3.
[0049] Referring to FIG. 4 showing a state of the displacement
control valve 30 when the compressor 100 is operating under an
intermediate load in the control range R1, the discharge pressure
correction rod 41 is moved in the direction of an arrow 72 with an
increase of the discharge pressure Pd while overcoming the urging
force of the spring 42. Thus, the pressing force to keep the valve
body 40 in closed position by the correction rod 41 is cancelled.
In this state of the discharge pressure correction rod 41, the
spring 63 is merely moved in the direction of the arrow 72 with the
correction rod 41, exerting no urging force. The valve body 40 is
moved off the valve seat 39 and, therefore, the first supply port
20a and the second supply port 23a become in communication with
each other, thereby allowing refrigerant under a high pressure in
the discharge chamber 4 to flow into the crank chamber 9 through
the second supply passage 23, the second supply port 23a, the first
supply port 20a and the first supply passage 20. As a result, crank
chamber pressure Pc is increased and the back pressure acting on
the pistons 18 is increased accordingly, so that the inclination
angle of the wobble plate 15 is decreased. Thus, the stroke length
of the pistons 18 is shortened, causing the displacement to be
reduced. Since the suction pressure Ps in the suction pressure
chamber 51 acts against F1, the force to open the valve body 40 is
decreased with an increase of the suction pressure Ps.
[0050] From the schematic diagram of FIG. 8 showing various forces
acting in the displacement control valve 30 while the compressor is
operating in the intermediate-load control range R1, the
equilibrium state of such forces can be expressed by equation (3),
and transforming this equation (3), the relationship between
suction pressure Ps and discharge pressure Pd can be expressed by
equation (4), as follows.
F1-S1.multidot.Ps+S2.multidot.Ps-S2.multidot.Pd=0 (3)
Ps=-{S2/(S1-S2)}.multidot.Pd+F1/(S1-S2) (4)
[0051] Expressing the equation (4) in a coordinate system with the
discharge pressure Pd and the suction pressure Ps represented by
abscissa and ordinate, respectively, the inclination of the line is
determined by -S2/(S1-S2). Since the cross-sectional area S1 is
greater than S2, or S1>S2, the inclination of the Pd Ps
characteristic line in the control range R1 is negative. That is,
the displacement control valve 30 provides Pd-Ps control
characteristic as shown by the line section L1 of FIG. 6 in the
intermediate-load control range R1. The variation of suction
pressure Ps with respect to discharge pressure Pd in the control
range R1 is referred to as the first variation in the
invention.
[0052] Now referring to FIG. 5 showing a state of the displacement
control valve 30 when the compressor 100 is operating under a high
load in the control range R2, the discharge pressure correction rod
41 is moved further in the direction of the arrow 72 with a buildup
of the discharge pressure Pd while overcoming the urging force of
the spring 42. With the correction rod 41 thus moved, the spring 63
begins to be compressed and to act against the force F2. After the
spring 63 has been fully compressed, the valve box 60 and the valve
body 40 are moved together with the discharge pressure correction
rod 41 in the direction of the arrow 72 which causes the valve body
40 to open. That is, in the high-load control range R2, the valve
body 40 is moved in its opening direction by cooperative action of
the correction rod 41, the valve box 60 and the spring 63.
[0053] From the schematic diagram of FIG. 9 showing various forces
acting in the displacement control valve 30 during compressor
operation in the high-load control range R2, the equilibrium state
of such forces is expressed by equation (5), and transforming this
equation (5), the relationship between suction pressure Ps and
discharge pressure Pd is expressed by equation (6), as follows.
F1-S1.multidot.Ps+S2.multidot.Ps-S2.multidot.Pd-S3.multidot.Ps+k.sub.3.mul-
tidot.x.sub.3-k.sub.2.multidot.x.sub.2+S3.multidot.Pd-F2=0 (5)
[0054] 1 F1 - S1 Ps + S2 Ps - S2 Pd - S3 Ps + k 3 x 3 - k 2 x 2 +
S3 Pd - F2 = 0 ( 5 ) Ps = - { ( S2 - S3 ) / ( S1 - S2 + S3 ) } Pd -
( k 2 x 2 - k 3 x 3 ) / ( S1 - S2 + S3 ) + ( F1 - F2 ) / ( S1 - S2
+ S3 ) ( 6 )
[0055] In the equation (6), the urging forces of the springs 42 and
63 are expressed by k.sub.2.multidot.x.sub.2 and
k.sub.3.multidot.x.sub.3, respectively, wherein x.sub.2 and x.sub.3
represent the distances by which the respective springs 42 and 63
are compressed.
[0056] In the illustrated embodiment, the displacement control
valve 30 operates in the high-load control range R2 such that Pd-Ps
characteristic is represented by the line section L2 which is
substantially flat as shown in FIG. 6. The variation of suction
pressure Ps with respect to discharge pressure Pd in the control
range R2 is referred to as the second variation in the invention.
It is noted that, since the values x.sub.2 and x.sub.3 are
dependent on discharge pressure Pd, the urging forces
k.sub.2x.sub.2 and k.sub.0x.sub.0 of the springs 42 and 63,
respectively, vary with discharge pressure Pd. Therefore, the
inclination of the line section L2 depends on the values of the
first and second terms of the right side of the equation (6).
[0057] As is now apparent from the foregoing, fuel consumption can
be improved by elevating the suction pressure Ps in the
intermediate-load control range R1 and also engine is not
overloaded by suppressing a decrease of the suction pressure Ps in
the high-load control range R2. In this control range R2, an
excessive temperature rise of coolant of a vehicle engine can be
prevented successfully. Thus, the proof stress of the compressor
100 can be ensured. As is apparent from FIG. 6, problems such as
mist formation on the windshield surface and evaporator frosting
which tends to occur in the low-load control range H3 can be
forestalled.
[0058] Additionally, the displacement control valve 30 makes it
possible to rationally control displacement of the compressor 100
in each of the control ranges R1, R2 and R3.
[0059] As is understood by those skilled in the art the present
invention is not limited to the above illustrated specific
embodiment, but it can be practiced in various forms and changes,
as exemplified below.
[0060] While in the above embodiment controlling is performed such
that suction pressure Ps is maintained substantially constant
irrespective of an increase in discharge pressure Pd in the
high-load control range R2, controlling of suction pressure Ps in
this range may be changed as required. For example, setting may be
made such that change of suction pressure Ps with respect to a rise
of discharge pressure Pd occurs in any combination of manners of
changes which include decreasing of suction pressure Ps at a third
variation which is smaller than the first variation in the
intermediate-load control range R1, increasing of suction pressure
Ps at a fourth variation and maintaining suction pressure Ps
substantially constant.
[0061] Referring to FIG. 10 showing a modification of the present
invention, a modified displacement control valve 130 is provided,
wherein like reference numerals or symbols designate like elements
or parts of the displacement control valve 30 of the preferred
embodiment.
[0062] The cylindrical housing 31 is formed with third supply ports
23b communicating with the second supply passages 23 in the main
valve body 33 and a discharge pressure chamber 152 as a discharge
region where discharge pressure Pd prevails due to the
communication of the above third supply port 23b and the second
supply passage 23. In this embodiment, the first supply passage 20,
the first supply port 20a, the second supply passage 23 and the
second supply port 23a and the third supply port 23b constitute the
communication routes of the variable displacement type compressor
according to the present invention. A discharge pressure correction
rod 141 is disposed within the discharge pressure chamber 152. The
stem portion 141b of this correction rod 141 has a cross-sectional
area S4. In the high-load control region R1, the discharge pressure
correction rod 141 acts on the bellows 36 in the direction of an
arrow 170, or rightward as seen in FIG. 10, against the urging
force of a spring 142 disposed in the discharge pressure chamber
152 and having a spring constant k.sub.4. These discharge pressure
correction rod 141 and the spring 142 are referred to as the urging
means of the invention. In operation in the high-load control range
R2, the discharge pressure correction rod 141 and the spring 142
cooperate to urge the valve body 40 in the direction that cause the
valve to open. In the control ranges R1 and R3, the displacement
control valve 130 operates in the same manner as the counterpart 30
of the preferred embodiment.
[0063] Equilibrium state of forces acting in the displacement
control valve 130 in the control range R2 is expressed by equations
(7) and (8) below, wherein k.sub.1 represents the spring constant
of the spring 36a and x.sub.1 represents the distances by which the
bellows 36 is contacted.
Ps=-{S1/(S1+S2)}Pd+(k.sub.1.multidot.x.sub.1)/(S1+S2)+F1/(S1+S2)
(7)
F1+k.sub.1.multidot.x.sub.1=(Pd-Ps).multidot.S4-k.sub.4.multidot.x.sub.4
(8)
[0064] In the equation (8), the contraction distance x.sub.4 and
hence the urging force k.sub.4.multidot.x.sub.4 of the spring 142
is dependent on discharge pressure Pd, the inclination of the line
section L2 for the high-load control range R2 depends on the values
of the first and second terms of the right side of the equation
(7).
[0065] Referring to FIG. 11 showing a further modification of the
present invention, this modification differs from the preferred
embodiment in the structure of valve box as the rod supplementing
member of the invention. The rod supplementing member of FIG. 11
includes a spring 80 and spring washers 81 and 82. The discharge
pressure correction rod 41 is disposed passing through a is
through-hole 82a formed in the spring washer 82. This rod
supplementing member can perform the same function as the
counterpart comprising the valve box 60 and the spring 63 of the
preferred embodiment. Additionally, the spring 80 and the spring
washer 82 may be substituted by a single member including a
modified spring.
[0066] The present examples and preferred embodiments are to be
considered as illustrative and not restrictive, and the invention
is not to be limited to the details given herein but may be
modified within the scope of the appended claims.
* * * * *