U.S. patent application number 10/592978 was filed with the patent office on 2008-08-28 for compressor, especially axial piston compressor for a vehicle air conditioning system.
Invention is credited to Henrick Brandes, Daniel Damson.
Application Number | 20080206074 10/592978 |
Document ID | / |
Family ID | 34960285 |
Filed Date | 2008-08-28 |
United States Patent
Application |
20080206074 |
Kind Code |
A1 |
Brandes; Henrick ; et
al. |
August 28, 2008 |
Compressor, Especially Axial Piston Compressor for a Vehicle Air
Conditioning System
Abstract
Compressor, especially an axial piston compressor for a vehicle
air-conditioning system, having a housing delimiting a drive
mechanism chamber (17), having a cylinder block in which at least
one piston is mounted so as to be axially displaceable back and
forth, and having a cylinder head having a suction side and a
delivery side, there being provided between the drive mechanism
chamber (17) and the suction side (18) a fluid connection (12, 13)
in which there is arranged a regulating valve (10) by means of
which, starting from a predetermined pressure difference between
the drive mechanism chamber (17) and the suction side (18), the
fluid connection between the drive mechanism chamber and the
suction side is increasingly throttled as the pressure difference
further increases, in order that the mass flow flowing out is
thereby maintained at an approximately constant low initial
level.
Inventors: |
Brandes; Henrick;
(Ludwigsburg, DE) ; Damson; Daniel; (Weissach,
DE) |
Correspondence
Address: |
ANDRUS, SCEALES, STARKE & SAWALL, LLP
100 EAST WISCONSIN AVENUE, SUITE 1100
MILWAUKEE
WI
53202
US
|
Family ID: |
34960285 |
Appl. No.: |
10/592978 |
Filed: |
January 5, 2005 |
PCT Filed: |
January 5, 2005 |
PCT NO: |
PCT/EP2005/000043 |
371 Date: |
May 5, 2008 |
Current U.S.
Class: |
417/307 |
Current CPC
Class: |
F04B 2027/1831 20130101;
F04B 2027/1859 20130101; F04B 2027/1845 20130101; F04B 27/1804
20130101; F04B 2027/1813 20130101 |
Class at
Publication: |
417/307 |
International
Class: |
F04B 49/24 20060101
F04B049/24 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 17, 2004 |
DE |
10 2004 013 096.5 |
Claims
1. Compressor, especially an axial piston compressor for a vehicle
air-conditioning system, having a housing delimiting a drive
mechanism chamber (17), having a cylinder block in which at least
one piston is mounted so as to be axially displaceable back and
forth, and having a cylinder head having a suction side and a
delivery side, there being provided between the drive mechanism
chamber (17) and the suction side (18) a fluid connection (12, 13)
in which there is arranged a regulating valve (10) by means of
which, starting from a predetermined pressure difference between
the drive mechanism chamber (17) and the suction side (18), the
fluid connection between the drive mechanism chamber and the
suction side is increasingly throttled as the pressure difference
further increases and is, in the extreme case, closed completely,
in particular the free cross-section of the fluid connection being
reduced in such a manner that the mass flow flowing out of the
drive mechanism chamber is maintained approximately at a constant
low level.
2. Compressor according to claim 1, characterised in that, in the
event of a predetermined higher pressure difference between the
drive mechanism chamber (17) and the suction side (18), the
regulating valve (10) reopens their fluid connection so that a
predetermined lower pressure difference can be established.
3. Compressor according to claim 1, characterised in that the
throttling behaviour of the regulating valve (10) with increasing
pressure difference between the drive mechanism chamber (17) and
the suction side (18) is linear, progressive, degressive and/or
stepped.
4. Compressor according to claim 1, characterised in that the
regulating valve (10) comprises a cylinder space (11), which has
fluid connections (lines 12, 13) with the drive mechanism chamber
(17), on the one hand, and with the suction side (18), on the other
hand, and within which a piston (14) is mounted so as to be
displaceable back and forth especially in each case against the
action of a resilient element (15, 16), wherein the piston (14), in
dependence on the pressure difference acting on the piston (14)
corresponding to the pressure difference between the drive
mechanism chamber (17) and the suction side (18), opens the fluid
passageway between the drive mechanism chamber and the suction side
to a greater or lesser extent, and in the extreme case closes it
completely.
5. Compressor according to claim 4, characterised in that the
piston (14) of the regulating valve (10) is a hollow piston open at
one end face, in the wall (19) of which there is formed at least
one axially extending, especially slot-shaped, passageway (20),
with which passageway (20) there is associated the suction side or
a fluid line (13) in communication with the suction side (18) and
opening out laterally into the cylinder space (11), whilst the
internal space (21) of the piston (14) has, by way of its open end
face (22), a fluid connection (line 12) with the drive mechanism
chamber (17).
6. Compressor according to claim 4, characterised in that the
suction side (18) is also applied to the closed end face of the
piston (14) or, that is to say, its piston base (23).
7. Compressor according to claim 4, characterised in that the
piston (14) of the regulating valve (10) is clamped between two
spring elements, especially helical compression springs (15, 16),
in contact with its end faces, within the cylinder space (11).
8. Compressor according to claim 7 characterised in that the spring
elements (15, 16) are integrally connected to the piston (14).
9. Compressor according to claim 4, characterised in that the wall
(19) of the piston (14) has a second passageway (27) which is
spaced axially away from the first passageway in the direction of
the delivery (high-pressure) side and which comes into effect after
a predetermined higher pressure difference between the drive
mechanism chamber (17) and the suction side (18) has been exceeded
and opens or frees the fluid connection between the drive mechanism
chamber and the suction side for reducing the higher pressure
difference.
10. Compressor according to claim 1, characterised in that in the
flow path of the regulating valve (10), especially in its piston
(14), there are arranged means for separating out lubricants,
particles or the like.
11. Compressor according to claim 1, characterised in that the
piston (14) of the regulating valve (10) is made from steel, steel
alloy, light metal, especially aluminium, and/or plastics
material.
12. Compressor according to claim 11, characterised in that, when
the piston (14) is made of plastics material, the spring elements
in contact with the end faces, especially the helical compression
springs (15, 16), are integrated into the plastics material by
casting or are embedded therein.
13. Compressor according to claim 5, characterised in that the
passageway (20) associated with the suction side (18) is located in
the wall (19) of the piston (14) within an inward bulge, especially
an annular inward bulge, and/or the opening of the fluid line (13)
opening laterally into the cylinder space (11) and in communication
with the suction side (18) is located within an outward bulge,
especially an annular outward bulge or annular groove, so that the
function of the regulating valve (10) is maintained even in the
event of rotation of the piston (14) about its longitudinal
axis.
14. Compressor according to claim 5, characterised in that on the
outside of the piston wall (19) and/or on the cylinder wall
delimiting the cylinder space there are formed one or more
longitudinal grooves, by means of which a fluid connection between
the suction side (18) and that part of the cylinder space which is
located beneath the piston base (23) is maintained.
15. Compressor according to claim 5, characterised in that the
slot-shaped passageway (20) in the wall (19) of the piston (14) of
the regulating valve (10) becomes wider or narrower either
continuously or stepped in one direction axially, in dependence on
the desired regulation behaviour, especially becoming narrower
either continuously or stepped towards the drive mechanism delivery
side, so that the mass flow flowing out of the drive mechanism
space remains substantially constant.
Description
[0001] The invention relates to a compressor, especially an axial
piston compressor for a vehicle air-conditioning system, having a
housing delimiting a drive mechanism chamber, having a cylinder
block in which at least one piston is mounted so as to be axially
displaceable back and forth, and having a cylinder head having a
suction side and a delivery side.
[0002] In specific terms, the compressor is a variable-capacity
compressor having a swash plate drive or wobble plate drive which
is located within the drive mechanism chamber and by means of which
the rotary movement of a drive shaft is converted into an axial
reciprocating movement of the piston or pistons. The swash plate or
wobble plate, also called in general manner a "tilt plate", is
variable in terms of its inclination relative to the drive shaft,
which can be coupled to an external motor. The inclination of the
"tilt plate" governs the stroke of the piston or pistons. When the
pressure in the drive mechanism chamber is relatively low, the
inclination of the "tilt plate" is large so that the stroke of the
piston or pistons is correspondingly long. When the pressure in the
drive mechanism chamber is relatively high, the inclination of the
"tilt plate" is small so that the stroke of the piston or pistons
is correspondingly short. With respect to the prior art, reference
may be made to the following publications: [0003] DE 196 11 004 A1
[0004] DE 44 41 721 C2 [0005] JP 2002/070739 A
[0006] Those publications relate in each case to steplessly
regulatable compressors having variable adjustment of the piston
stroke.
[0007] Such compressors are usually constructed in the form of
axial piston compressors, with modification of the stroke--as
already mentioned--being accomplished by means of a change in the
tilt angle of the "tilt plate". In the process, the position of the
lower dead centre of the piston or pistons is changed; the location
of the upper dead centre and, as a result, the size of the
so-called clearance volume remains unchanged in the idealised
case.
[0008] In operation of such a compressor, internal leaks and losses
usually occur. The main cause thereof is that, in the course of
compression of a coolant drawn into the cylinder or cylinders, a
so-called partial mass flow usually enters the drive mechanism
space of the compressor through the gap between the cylinder and
piston. This effect is also known as "blow-by". Insofar as an oil
separator is arranged on the high-pressure side of the compressor,
there is a possibility that coolant will, in undesirable manner,
enter the drive mechanism chamber by way of the oil return. In
order to avoid an undesirable over-pressure in the drive mechanism
chamber, there is provided between the drive mechanism chamber and
the low-pressure side, or suction side, a fluid connection by way
of which leak masses entering the drive mechanism chamber can flow
out again. The mentioned fluid connection is usually a connecting
bore. The free cross-section of that bore is generally so
dimensioned that, even under most unfavourable conditions, no
undesirable over-pressure arises in the drive mechanism chamber.
Because of the described dependency of the piston stroke on the
pressure within the drive mechanism chamber it is usual for the
compressor to be externally regulated by influencing the pressure
in the drive mechanism chamber. An increase in pressure inside the
drive mechanism chamber brings about an effect on the internal
force and moment equilibrium of the compressor such that the stroke
of the pistons is reduced. The compressor is, as a result,
"down-regulated". The converse occurs in the case of reduction of
pressure in the drive mechanism chamber. As a result, the
compressor can be "up-regulated". The corresponding regulating
valves in the prior art are electrically controlled. In the
process, increasing the pressure within the drive mechanism chamber
and, as a consequence, corresponding "down-regulation" of the
compressor are accomplished by appropriate opening of a fluid
connection between the drive mechanism chamber and the delivery
side, or high-pressure side, of the compressor. Arranged in that
fluid connection is the mentioned regulating valve, which is
preferably electrically controllable. In the process, it should be
ensured that the pressure in the drive mechanism chamber does not
exceed a predetermined maximum level. For that purpose, a safety
fluid connection is provided between the drive mechanism chamber
and the suction side of the compressor.
[0009] The pressure in the drive mechanism chamber can be adjusted
between the high pressure prevailing on the delivery side and the
low pressure prevailing on the suction side. The compressor can be
up-regulated and down-regulated within those limits. Increasing the
pressure in the drive mechanism chamber is of course always
accomplished in the prior art in relation to the pressure increase
by way of a fluid connection of constant cross-section between the
drive mechanism chamber and the suction side of the compressor. In
this context it is to be borne in mind that when maintaining the
increased differential pressure, owing to the constant
cross-section of the mentioned fluid connection, when
down-regulating the compressor, that is to say when increasing the
differential pressure between the drive mechanism chamber and the
suction side, the mass flow flowing out of the drive mechanism
chamber becomes continuously and significantly greater. Because
that mass flow has to be taken directly from the high-pressure
side, it is no longer available in the system for the actual
purpose of the compressor, that is to say cooling or heating, and
must consequently be regarded as a loss. The mass flow required for
down-regulating the compressor is conveyed, almost exclusively by
internal compressor means, from the high-pressure side, by way of
the regulating valve, to the drive mechanism chamber and from
there, through the fluid connection between the drive mechanism
chamber and the suction side, back to the suction side, from where
is it is again drawn in and compressed. Additional outlay which
provides no direct benefit is required for compression of that
so-called "regulating mass flow".
[0010] By way of example, FIG. 1 illustrates the above-mentioned
behaviour. As the pressure difference between the drive mechanism
chamber and the suction side increases (X axis), the mass flow
through the fluid connection between the drive mechanism chamber
and the suction side increases significantly. In addition to the
loss mass flow, the associated inlet and outlet pressures before
and after the fluid connection or opening between the drive
mechanism chamber and the suction side are also shown, as well as,
by way of example, a possible temperature plot at the inlet. All
the curve plots are to be regarded merely as examples; however, the
basic behaviour for all typical operating points of a compressor
for a vehicle air-conditioning system can be recognised. The
starting point of the mass flow curve, located at a low pressure
difference between the drive mechanism chamber and the suction side
and at a corresponding low mass flow, is defined substantially by
internal leakage and other factors which will not be described in
greater detail here. The free cross-section of the fluid connection
between the drive mechanism chamber and the suction side is usually
so selected that, for all the operating states that are to be
assumed, undesired down-regulation of the compressor does not come
about.
[0011] Especially in central Europe, with comparatively moderate
average annual temperatures and relatively low average atmospheric
humidity, air-conditioning systems used in particular in the motor
vehicle sector are frequently down-regulated (with the
above-mentioned inherent losses caused by the down-regulation). The
present invention is intended to provide a simple, efficient and
economical solution to that problem in particular.
[0012] A further problem besides the energy losses is posed by the
loading of the pistons and of the "tilt plate mechanism". The
pressure-related main direction of force in compressors is axial,
from the upper side of the piston to the underside of the piston.
The opposite loading case (in the direction of the upper side of
the piston) occurs, as a result of pressure, significantly only in
the case of down-regulation of the compressor, that is to say in
the case of an increase in pressure in the drive mechanism chamber
above the pressure of the suction side. Therefore, in
down-regulated operation it must be ensured that the
pressure-related forces acting on the underside of the piston do
not exceed a defined level. In this context it must also be borne
in mind that, preferably, pistons made of light materials,
especially light metal, are to be used, which are advantageous both
in energy terms and in regulation terms. The present invention is
intended to provide a possible solution under this aspect too.
[0013] Consequently, the problem underlying the present invention
is to minimise the loss mass flow that occurs during
down-regulation, in particular in the case of an externally
regulated compressor having any regulation characteristic, and, on
the other hand, to provide a safety device which is capable of
limiting or reducing the pressure-related forces acting in the
direction of the upper side of the piston during the intake
process.
[0014] In the case of a compressor of the kind mentioned at the
beginning, the problem is solved in accordance with the invention
by means of the fact that there is provided between the drive
mechanism chamber and the suction side a fluid connection in which
there is arranged a continuously operating regulating valve by
means of which, starting from a predetermined pressure difference
between the drive mechanism chamber and the suction side, the fluid
connection between the drive mechanism chamber and the suction side
is increasingly throttled as the pressure difference further
increases and is, in the extreme case, closed completely.
[0015] The "constant" opening provided between the drive mechanism
chamber and the suction side in the prior art is accordingly
replaced, in accordance with the invention, by a "variable
opening", more particularly in regulation terms in such a way that
the opening cross-section is increasingly reduced as the
differential pressure between the drive mechanism chamber and the
low-pressure side, or suction side, increases, as a result of which
the loss mass flow can be kept almost constant at the original
value.
[0016] Preferably, the regulating valve in the fluid connection
between the drive mechanism chamber and the suction side opens
again in the event of a predetermined excessively high pressure
difference between the drive mechanism chamber and the suction side
so that damage to or destruction of the pistons is countered.
Accordingly, the basic concept is that, in the event of an
excessively high pressure difference between the drive mechanism
chamber and the suction side, at least one opening which is not
active in normal operation comes into effect, through which opening
a flow of mass out from the drive mechanism chamber is possible in
such a way that the pressure in the drive mechanism drops back to a
lower operating pressure. This measure is a safety measure in order
to protect the compressor, or drive mechanism chamber, from
undesirable over-pressure.
[0017] Further details of the invention, especially constructional
details, are given in claims 3 ff. Reference will also be made to
those details separately in the course of the following description
of the invention, especially using examples of embodiments. In that
respect, reference is made to the accompanying drawings, in
which:
[0018] FIG. 2 shows the influence of various temperatures on the
loss mass flow;
[0019] FIG. 3 shows, in diagrammatic form, a first arrangement of a
regulating valve constructed and arranged in accordance with the
invention, between the drive mechanism chamber and the suction side
of a compressor (normal operating state);
[0020] FIG. 4 shows the typical down-regulation curve of an
externally regulated compressor;
[0021] FIG. 5 shows a possible force plot within a mechanical
regulating valve according to the invention during
down-regulation;
[0022] FIG. 6 shows a comparison of the loss mass flows through a
fluid connection between the drive mechanism chamber and the
suction side, the cross-section of the opening of which is variable
by means of the regulating valve according to the invention;
and
[0023] FIG. 7 shows the arrangement according to FIG. 3 with
activated safety function.
[0024] If one considers the loss mass flow for typical operating
conditions of a compressor, especially an axial piston compressor
for vehicle air-conditioning systems, it can be seen that, for a
down-regulation range, the influence of various temperatures and
inlet conditions is small. Rather, as can be seen from FIG. 2, it
is the pressure difference between the inlet side and outlet side
of a regulating valve arranged in a fluid connection between the
drive mechanism chamber and the suction side that is decisive for
the mass flow that flows out.
[0025] If a medium condition is taken as dimensioning reference,
for the usual down-regulation range generally the maximum
difference of the actually occurring "extreme points" is less than
about 2% (in relative terms) for the usual down-regulation
range.
[0026] The fact that the differential pressure between the drive
mechanism chamber and the suction side is substantially responsible
for the loss mass flow can be exploited by means of a mechanical
regulating valve according to FIG. 3. Accordingly, the regulating
valve 10 comprises a cylinder space 11, which has, on the one hand,
a fluid connection, by way of a line 12, with the drive mechanism
chamber of an axial piston compressor and, on the other hand, a
fluid connection, by way of a further line 13, with the suction
side of the compressor and within which a piston 14, closed on the
low-pressure side, is mounted so as to be displaceable back and
forth in each case against the action of a resilient element--in
this instance helical compression springs 15, 16--and of the forces
caused by the inlet and outlet pressure, wherein the piston 14, in
dependence on the pressure difference acting on the piston 14
corresponding to the pressure difference between the drive
mechanism space (indicated by reference numeral 17 in FIG. 3) and
the suction side (indicated by reference numeral 18 in FIG. 3),
reduces the effective valve opening between the drive mechanism
space and the suction side to a greater or lesser degree, and in
the extreme case closes it completely. The mentioned fluid
passageway is defined by the lines 12, 13 and also the cylinder
space 11 and the piston 14, which for the purpose is in the form of
a hollow piston open at one end face (the upper end face in FIG.
3), in the wall 19 of which there is formed at least one axially
extending, especially slot-shaped, passageway 20, with which
passageway 20 there is associated the suction side 18 or a fluid
line 13 in communication with the suction side 18 and opening out
laterally into the cylinder space 11. The internal space 21 of the
hollow piston 14 has a fluid connection with the drive mechanism
chamber 17 by way of the open end face 22. On the suction side, the
piston 14 is closed off by a piston base 23. The suction side, that
is to say low pressure, is applied externally to that piston base
23. For that purpose, the cylinder space 11 below the piston base
23 is in communication by way of a connecting line 24 with the
suction side, or with the line 13 leading to the suction side.
[0027] The piston 14 is clamped between two springs, in this
instance helical compression springs 15, 16, in contact with its
end faces, within the cylinder space 11. The cylinder space 11 is
defined by a corresponding bore in a valve body 25, the opening of
the bore being closed off by means of a stopper 26 after the
helical compression springs and the piston 14 have been put in
place.
[0028] The spring elements 15, 16 are so constructed and adjusted
that the throttling behaviour of the regulating valve 10 with
increasing pressure difference between the drive mechanism chamber
17 and the suction side 18 is either linear or progressive,
degressive and/or stepped. This is also dependent on the formation
of the passageway 20 in the piston 14. The slot-shaped passageway
20 in the wall 19 of the piston 14 can be constructed in the form
of a slot that becomes wider or narrower either continuously or
stepped in one direction axially, more specifically in accordance
with the desired regulation behaviour. In order to achieve a
constant mass flow, a geometry that becomes continuously narrower
in the axial direction is to be provided.
[0029] The valve body 25 can be part of the compressor housing or a
separate component. When the piston 14 is made of plastics
material, the springs 15, 16 are preferably provided integrally
with the piston as a structural unit, that is to say are integrated
with the piston material at the end faces by casting. As already
mentioned, the piston 14 is installed within the cylinder space 11
with biasing by the two spring elements 15, 16 so that the springs
are in contact with the piston 14 in all operating states.
[0030] The piston 14 is fitted inside the cylinder space 11 with a
play fit, more specifically preferably with a fit of less than 15
.mu.m, in order to keep the mass flow flowing past the piston at a
negligibly low level. In order to achieve this, additional sealing
measures can be provided between the piston and the cylinder
wall.
[0031] In FIG. 3, the piston 14 is constructed with identical end
faces. It is also feasible to use a differential piston having end
faces of different sizes instead, this being governed by which
forces, especially differential forces, are acting on the piston.
The spring forces produced by the spring elements 15, 16 are, in
contrast, of subordinate importance. In that respect reference is
made to FIG. 5.
[0032] When the pressure between the drive mechanism chamber and
the suction side is balanced, the piston 14 is held in a middle
position. The passageway 20 provided in the piston wall 19 is then
located at approximately the same height as the line 13 leading to
the suction side 18.
[0033] Usually a minimum differential pressure between the drive
mechanism chamber and the suction side is necessary in order to
bring about a reduction in the compressor stroke. This minimum
differential pressure should be taken into account when designing
the described mechanical regulating valve. Firstly, in terms of
design, the slot-shaped passageway(s) 20 incorporated in the piston
wall 19 should, as far as possible, be so positioned that, in the
case of the mentioned minimum pressure difference, the full area of
the passageway(s) 20 is effective. A further increase in the
differential pressure should, however, result as immediately as
possible in successive reduction of the effective opening
cross-section of the slot-shaped passageway(s) 20.
[0034] The design of the passageway opening in the piston wall 19
should be such that internal leaks, or other factors which will not
be described in greater detail here, can flow out completely by way
of the piston 14, or regulating valve 10, in the case of a minimum
pressure difference between the drive mechanism chamber and the
suction side.
[0035] In the course of the down-regulation procedure, the
differential pressure between the drive mechanism chamber and the
suction side increases. A possible force plot of spring and
pressure forces in the regulating valve 10 in the case of
increasing differential pressure and corresponding displacement of
the piston 14 (downwards in FIG. 3) is shown by way of example in
FIG. 5, in which it is also assumed that, in the course of
down-regulation, an increase in the low pressure on the suction
side also comes about.
[0036] The regulating valve 10 can have any desired installation
position, because the weight of the piston 14 itself is negligible
for regulation. The regulating valve 10 can be arranged at the
cylinder head or cylinder block or, taking appropriate connections
into account, outside the compressor housing.
[0037] As can also be seen from FIG. 5, the regulating piston 14
moves towards the suction side as the differential pressure
increases. As a result, the slot-shaped passageway 20 in the piston
wall 19 is increasingly covered over and, correspondingly, the
opening cross-section is increasingly reduced. The passageway 20 is
preferably so constructed that after displacement of the piston 14
there remains a residual opening cross-section such that an almost
constant mass flow is established between the drive mechanism
chamber and the suction side. In that respect reference is made to
FIG. 6.
[0038] Because the mass flow flowing out with the aid of the
described regulating valve 10 during down-regulation can generally
be maintained at an approximately constant low level (see FIG. 6),
a significantly lower loss mass flow is required in down-regulated
operation in order to establish the differential pressure between
the drive mechanism chamber and the suction side that is required
for down-regulation. As a result, comparatively less drive power
has to be expended for the same cooling or heating performance. The
efficiency is consequently increased, more specifically for the
entire down-regulation range, the relative loss mass flow being
increasingly reduced as the differential pressure between the drive
mechanism chamber and the suction side increases.
[0039] In the case of the arrangement according to FIG. 7, a
further opening, or a so-called safety slot 27, is provided in the
piston wall 19 above the slot-shaped passageway 20, that is to say
in the direction of the delivery side, which comes into effect
immediately when the lower slot-shaped passageway 20 has been
completely covered over, more specifically when the pressure in the
drive mechanism space becomes excessively high and the piston 14 in
the regulating valve 10 is consequently displaced further to the
suction side. The safety slot 27 therefore comes into effect when
the differential pressure between the drive mechanism chamber and
the suction side reaches a predetermined maximum value. The
pressure in the drive mechanism chamber can then be effectively and
rapidly reduced to a lower operating pressure by way of the safety
slot 27.
[0040] In other respects, the regulating valve according to FIG. 7
is constructed correspondingly to that according to FIG. 3, and
elements that have already been described with reference to FIG. 3
are indicated in FIG. 7 by the same reference numerals.
[0041] As a result of the regulating valve described, a further
advantage is also achieved, namely the advantage that the mass flow
between the drive mechanism chamber and the suction side of the
compressor is greatly reduced. As a result, the oil mass flow, that
is to say the amount of oil carried along with the gas flow, is
also correspondingly reduced. This on the one hand has a positive
effect on the overall performance and also on the thermal behaviour
of the compressor and, as a result, that of a vehicle
air-conditioning system and on the other hand has an advantageous
effect on the service life of the compressor.
[0042] The described regulating valve can be provided in the form
of a prefabricated structural unit. Further elements, such as oil
separators, particle filters or the like, can be integrated within
the piston or also within the cylinder space.
[0043] The valve body 25 is preferably made of steel, steel alloy,
light metal, especially aluminium, or also plastics material. The
same applies to the piston 14. When the piston 14 is made of
plastics material it is possible for the spring elements 15, 16 to
be intimately or permanently connected to the piston material so
that the piston and spring elements form a structural unit which
can be introduced as one entity into the cylinder space 11. When
the piston 14 is made of plastics material, manufacture by
injection-moulding, above all, is advantageous. Thermosetting
plastics or thermoplastic materials can be used. In the case of
injection-moulding, the passageway slots 20 and 27 can be formed in
one operation. Plastics material optimised in terms of sliding
properties, especially thermosetting plastics or thermoplastic
materials optimised in terms of sliding properties, can be
used.
[0044] When metallic materials are used for the piston 14, the
passageways 20, 27 are formed preferably by laser (laser cutting).
By that means any desired contours and opening cross-sections can
be obtained. As already mentioned, the slot-shaped passageway 20 in
the wall 19 of the piston 14 can become wider or narrower either
continuously or stepped in one direction axially, in dependence on
the desired regulation behaviour, with preference being given in
this case to the narrowing geometry. The contour of the passageway
20 is finally also dependent on the compressor itself and its
operating behaviour.
[0045] The fluid line 12 in communication with the drive mechanism
chamber 17 can of course also be so arranged that it opens out into
the cylinder space 11 axially. To that extent, FIGS. 3 and 7 are
merely diagrammatic representations of the general principle. In
other words, the inlet opening into the cylinder space 11 can, if
required, also be provided through the closure stopper 26. In the
region of the mouth of the line 13, which leads to the suction
side, there can be provided an outward bulge, which ensures that
gas can flow out through the passageway 20 even when the piston 14
rotates about its longitudinal axis. In corresponding manner, the
passageway 20 can also be positioned within an inward bulge,
especially an annular inward bulge, in the piston wall 19. It is
also possible to provide a plurality of passageways 20 in the
piston wall 19, which are arranged distributed over the
circumference of the piston. Preference is given, however, to the
piston 14 being positioned within the cylinder space 11 so that it
is secured against rotation.
[0046] The connection between the outside of the piston base 23 and
the suction side can, moreover, be made directly by way of the
piston 14, more specifically by way of longitudinal grooves formed
on the piston or on the cylinder wall. These pressure-communicating
grooves are accordingly intended to make a fluid connection between
the suction side and the space beneath the piston base 23. In order
to ensure that this is the also the case in any desired axial
position of the piston 14, the corresponding grooves are preferably
formed on the cylinder wall. Pressure-communicating grooves of such
a kind also have the advantage of improved axial mobility of the
piston 14. Oil carried along by the coolant, which might otherwise
impair the mobility of the piston 14 within the cylinder space 11,
accumulates within the pressure-communicating longitudinal or axial
grooves. By means of the mentioned longitudinal or axial grooves,
therefore, the contact area between the piston and the cylinder
wall is reduced on the one hand. On the other hand, an
oil-collecting space is created so that the oil--especially at low
ambient temperatures--does not hinder the mobility of the piston 14
within the cylinder space 11. The risk of the piston 14 being
restricted in terms of its freedom to move within the cylinder
space 11 is reduced. In addition, it is ensured that the pressure
difference between the drive mechanism chamber and the suction side
is applied to the piston 14 without having to provide an additional
connection with the low-pressure side.
[0047] There are three significant positions of the piston 14:
[0048] middle position in the case of pressure balanced between the
drive mechanism chamber and the suction side (the opening
cross-section of the passageway 20 in the piston wall 19 being
fully effective) [0049] working point with application of pressure
difference between the drive mechanism chamber and the suction side
(the opening cross-section of the passageway 20 being reduced)
[0050] safety position in the case of an undesirably high pressure
difference between the drive mechanism chamber and the suction side
(only the safety slot 27 being effective)
[0051] All features disclosed in the application documents are
claimed as being important to the invention insofar as they are
novel on their own or in combination compared with the prior
art.
REFERENCE NUMERALS
[0052] 10 regulating valve [0053] 11 cylinder space [0054] 12 line
[0055] 13 line [0056] 14 piston [0057] 15 helical compression
spring [0058] 16 helical compression spring [0059] 17 drive
mechanism space [0060] 18 suction side [0061] 19 piston wall [0062]
20 (slot-shaped) passageway [0063] 21 internal space [0064] 22 open
end face [0065] 23 piston base [0066] 24 connecting line [0067] 25
valve body [0068] 26 closure stopper [0069] 27 safety slot
* * * * *