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Description  |
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TECHNICAL FIELD
The present invention relates to variable displacement axial compressors,
and more particularly, to an assembly providing pressure pulse attenuation
for pressurized discharge gas and the related method, resulting in
smoother operation and extended service life of the compressor.
BACKGROUND OF THE INVENTION
A variety of refrigerant compressors for use in vehicle air conditioning
systems are currently available. A popular vehicle compressor design is
the variable displacement axial type. In this type of compressor, a number
of cylinders are equally angularly spaced about and equally radially
spaced from the axis of a central drive shaft. A piston is mounted for
reciprocal sliding motion in each of the cylinders. Each piston is
connected to a swash plate or wobble plate received about and operatively
connected to the drive shaft. During operation of the compressor, rotation
of the drive shaft imparts a wave-like reciprocating motion to the wobble
plate. This driving of the wobble plate in a nutating path about the drive
shaft serves to impart a linear reciprocating motion to the pistons. By
varying the angle of the wobble plate relative to the drive shaft, the
stoke of the pistons and, therefore, the displacement or capacity of the
compressor may be varied to effect the desired compressing action.
A shortcoming realized in this type of compressor system is the degraded
performance resulting from gas pressure pulsations discharged from the
compressor. While the piston type compressor provides an effective way to
compress and circulate the refrigerant fluid throughout the system, it has
the adverse side effect of delivering high pressure pulsations coincident
with the discharge stroke of the pistons. In addition to creating a
noisier and rougher operating system, these discharge pressure pulsations
also lead to premature fatigue and failure of component parts throughout
the air conditioning system, thereby diminishing its reliability.
Various attempts have been made to reduce these pressure pulsations in
order to provide smoother and quieter running systems. One accepted
approach is to provide a restriction, such as a restricted nozzle, in the
discharge port of the compressor. As another example, U.S. Pat. No.
4,652,217, issued Mar. 24, 1987, to Shibuya shows a compressor with an
attenuation device in the form of a porous plug in the valve plate (see
FIGS. 4 & 5). This attenuation device operates in the same manner as a
standard restricted orifice by limiting the rate that gas is permitted to
escape the discharge chamber. This discharge rate is regulated by the size
and number of the restriction holes provided in the porous plug. The
system is configured such that, during the piston discharge stroke, a much
greater volume of fluid is discharged from the cylinder bore into an
intermediate discharge cavity than the restriction holes allow to pass
through the valve plate to the final discharge chamber. This results in a
variable pressurized region within the intermediate discharge cavity. This
pressure buildup is evidenced during the piston intake stroke by a
continual, and thus somewhat smoothed flow of pressurized gas to, and
consequently from the discharge chamber to the outlet port. In this way,
the net effect of the restriction is to stretch the compressor discharge
over the entire operational cycle (both intake and discharge strokes),
rather than just during the discharge stroke. The restriction also
provides some attenuation by interaction of the established stream
pulsations with incident pressure waves adjacent the restriction. This
action works by cancellation of opposing fluid forces, as is well known.
A different type of attenuation assembly is shown in U.S. Pat. No.
4,274,813 to Kishi et al., issued Jun. 23, 1981, in which a plurality of
baffles or dividers are provided in cascade fashion within the discharge
chamber. These baffles have a similar effect on the pressure pulsations
resulting from the discharge stroke of the piston, as did the restriction
holes in the Shibuya patent. That is, they provide a restriction so as to
prevent the fluid pulses from freely propagating through the discharge
chamber to the outlet port of the compressor. The result is a similar
buildup of pressure within the discharge chamber during the piston
discharge stroke. The increased pressure, like in the Shibuya patent, is
bled away during the piston intake stroke, thereby spreading the discharge
over the entire operational cycle. Also, to some extent the pulsations and
incident pressure waves cancel each other out, as in the other
arrangements.
While these design approaches have realized performance and reliability
improvements over other attempts, they enjoy only limited success. One
reason for this limitation is due to the constant or static orifice area
provided for the fluid discharge by the restriction hole(s) or baffles.
More specifically, and as elementary laws of fluid dynamics confirm, the
volumetric rate at which fluid is transferred in a compressor from the
discharge chamber through the outlet port and into the outgoing
refrigerant line is directly proportional to the pressure differential
between the discharge chamber and the refrigerant line, as well as the
size of the orifice area connecting the two. Therefore, in order to
maintain a substantially constant pressure at the output port and within
the refrigerant line, and thus maximize attenuation of pulses, the area of
the connecting orifice should be variable and controlled according to the
changing pressure within the discharge chamber. It is readily observed
that any design approach providing only a static or constant area orifice
still exhibits notable pressure pulsations at the output. Accordingly, a
need clearly exists for a design with a variable orifice to further reduce
the gas pressure pulsations from a compressor.
SUMMARY OF THE INVENTION
It is accordingly a primary object of the present invention to provide an
assembly for a fluid compressor and related method utilizing a variable
flow orifice that more efficiently attenuates pressure pulsations for
smoother and quieter operation.
Another object is to provide an improved pressure pulsation attenuation
assembly in an automotive air conditioning compressor and method that
provides a variable orifice under active control to smooth the flow from
the discharge port of the compressor.
Still another object of the present invention is to provide a pressure
pulsation attenuation assembly in an automotive air conditioning
compressor having an active control valve to provide a variable flow and
increased pulsation attenuation or dampening over that of the former
static attenuators described above.
Yet another object of the present invention is to provide an improved
pressure pulsation attenuation assembly in an automotive refrigerant
compressor including an active control valve comprising a timing plate
with specially shape orifice located in the discharge chamber and working
in conjunction with the outlet port, thus resulting in pulsation
attenuation and in smoother and quieter operation.
Additional objects, advantages and other novel features of the invention
will be set forth in part in the description that follows and in part will
become apparent to those skilled in the art upon examination of the
following or may be learned with the practice of the invention. The
objects and advantages of the invention may be realized and obtained by
means of the instrumentalities and combinations particularly pointed out
in the appended claims.
To achieve the foregoing and other objects, and in accordance with the
purposes of the present invention as described herein, an improved
pressure pulsation attenuation assembly is provided for a compressor
utilizing a variable orifice to regulate the flow. The attenuation
assembly is particularly useful to attenuate or dampen pulses resulting
from the operation of a piston type compressor. In its broadest aspects,
the present invention relates to a system for active control of the flow
from the compressor outlet port. In response to pressure pulses or changes
within the discharge chamber, the variable orifice is varied or adjusted
from partially restricted to wide open to thereby smooth the flow.
More particularly, the pressure within the discharge chamber normally
fluctuates during a single operational cycle in a predictable and periodic
fashion, such that it is at a maximum at the completion of each discharge
stroke and a minimum during the intake stroke. Utilizing this knowledge to
achieve maximum pressure pulsation attenuation, an active valving means is
provided that variably controls and regulates the flow to the outlet port
in proper timing and synchronization with each operational cycle of the
compressor.
In the preferred embodiment, the valving means includes a timing plate or
rotatable disc centrally attached to the compressor drive shaft, whereby
rotation of the drive shaft is imparted to the timing plate. In this way,
rotation of the timing plate is synchronized with each reciprocating
piston in the cylinder bores. That is, since all of the pistons of the
compressor cycle through one complete discharge stroke and one complete
intake stroke for each revolution of the drive shaft, and assuming proper
orientation of the timing plate on the drive shaft, the timing plates
movement is synchronized with the pistons.
The plate is characterized by a plurality of flow orifices that are
angularly spaced about a constant radius from the central longitudinal
axis. The angular spacing corresponds to the spacing between the operating
cylinders. The radius is determined such that the flow orifices line up or
coincide with the outlet port.
The timing plate is spaced by a predetermined gap from the lip of the
outlet port. During each compression stroke when the maximum flow of
pressurized fluid is coming from one of the cylinder bores, the plate thus
partially covers and restricts the flow to the outlet port.
When the flow from the cylinders is reduced, the corresponding flow orifice
aligns with the outlet port. Each flow orifice provides increasing flow
generally tracking the decreasing pressure in the discharge chamber, as
will be evident from the discussion below. To put it another way, rotation
of the timing plate during compressor operation effectively serves to
variably cover and uncover the outlet port spreading the flow over the
full cycle and thus offsetting the pressure fluctuations.
The valving means is tuned by selecting the proper length of the solid
portion and the length of overlap between the outlet port and the flow
orifices of the timing plate. In its broadest aspects, the outlet port and
the timing plate flow orifices may be the same size and shape.
More particularly, assume that initially a solid portion of the timing
plate coincides with the outlet port, such that the outlet port is
completely covered except for the gap between plate and the lip of the
port. The pressurized gas flow is restricted to a flow ring around the
port. As the orifice of the timing plate rotates into alignment with the
outlet port, the discharge of the gas is increased. The flow-through area
incrementally increases in size until the plate rotates into such a
position that precise alignment between the orifice and the outlet port
occurs. At this point, the flow-through area to the port is at a maximum.
Accordingly, as the timing plate continues to rotate and the orifice
rotates out of alignment with the outlet port, the corresponding
flow-through area is incrementally decreased until the outlet port is
again covered.
As previously discussed, pressure pulsations of the pressurized output
fluid at the outlet port are substantially eliminated if a substantially
constant volumetric fluid discharge rate therefrom is maintained. In
operation and in accordance with the related method of the invention, this
is accomplished by the outlet port being covered during the compression
stroke of the piston in the cylinder bore, and more particularly, covered
when the discharge reed valve of the discharge port of the cylinder is
open. The pressure pulsation is thus attenuated and a baseline flow rate
established as the gas forces its way into the outlet port via the flow
ring around the outlet port. Once this initial pressure pulse is
attenuated, the discharge flow rate is maintained by the flow orifice
being gradually uncovered in proportion to the decreasing residual
pressure in the discharge chamber. When the timing plate again covers the
outlet port, the discharge reed valve on the next in-line cylinder is set
to open, and the operational cycle repeats itself.
It should be further appreciated that in accordance with the more limited
principles of the invention, an infinite number of variations between the
size and shape of the discharge port and the timing plate orifices can be
implemented to achieve desirable results. However, in the present
preferred embodiment, and for both economic efficiency of this disclosure
and better retrofitability to existing compressors, the round shape of the
outlet port is left unchanged. This provides for adaptation of the present
invention to a variety of different model compressors at minimal cost.
Also, in the preferred embodiment, the present invention utilizes generally
pear-shaped orifices in the timing plate. Each orifice is oriented such
that, as the plate rotates, the narrow end of the orifice leads into the
alignment or overlap with the outlet port. Accordingly, the wide end is
the last to overlap with the outlet port. The net effect of this
arrangement is to provide a relatively small direct flow-through orifice
area immediately after the discharge reed valve closes and during the
early portion of the intake stroke (while discharge cavity pressure is
still relatively high). The flow-through orifice area continues to
increase the effective discharge area as the intake stroke progresses
(progressively lower discharge chamber pressurization). This in effect
gives a smooth, generally even flow from each cylinder, which when mixed
with the residual flow from the other cylinders in the discharge chamber,
eliminates the undesirable spiking of pressures and smooths the flow.
In addition to the improved results due to this flow control, the
advantageous pulsation/incident pressure wave interaction is also
improved. Especially during maximum pressure pulsation when the discharge
reed valve is open, the interacting solid portion of timing plate and the
lip of the outlet port, provide increased reflected pressure waves as the
flow reverses and flows behind the plate to exit as the flow ring. The
cancelling effect of the established flow stream and these pressure waves
of opposite and angular vectors is thus more effective, and as indicated
above is spread out over a longer time period. Also the rotation of the
timing plate sets up turbulent boundary layer flow providing additional
flow vectors to intercept and attenuate the primary pulses of gas from the
cylinders.
This active and controlled attenuation of the pressure pulsations at the
outlet port of the compressor, provides for a smoother and quieter running
compressor. Since unchecked pressure pulsations induce secondary
vibrations in the air conditioning system and the vehicle itself, a
reduction in the pulsations in the compressor accordingly smooths the
entire vehicle operation. Therefore, component fatigue and failure in the
air conditioning system resulting from such vibrations are reduced,
thereby increasing the useful life of the system. Additionally, the
smoother and quieter running system and vehicle, certainly provides
increased customer satisfaction.
Still other objects of the present invention will become apparent to those
skilled in this art from the following description wherein there is shown
and described a preferred embodiment of this invention, simply by way of
illustration of one of the modes best suited to carry out the invention.
As it will be realized, the invention is capable of other different
embodiments and its several details are capable of modification in
various, obvious aspects all without departing from the invention.
Accordingly, the drawings and descriptions will be regarded as
illustrative in nature and not as restrictive.
BRIEF DESCRIPTION OF THE DRAWING
The accompanying drawing incorporated in and forming a part of the
specification, illustrates several aspects of the present invention and
together with the description serves to explain the principles of the
invention. In the drawing:
FIG. 1 is a cross sectional side view of the entire compressor showing the
location of the active valving means, and with the orientation of the
timing plate relative to the outlet port during the time period when the
discharge reed valve is open, such that the outlet port is partially
covered by the solid portion of the plate;
FIG. 2 is a cross sectional side view, like FIG. 1, showing the timing
plate in a position such that the variable flow orifice and the outlet
port are aligned and fully open; and
FIG. 3 and 3a are front views of the timing plate showing the shape of the
flow orifices and positioning relative to the outlet port corresponding to
FIGS. 1 and 2, respectively.
Reference will now be made in detail to the present preferred embodiment of
the invention, an example of which is illustrated in the accompanying
drawing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Reference is now made to FIG. 1 illustrating a cross section of a variable
displacement wobble plate compressor 10 including an attenuation assembly
constructed in accordance with the teachings of the present invention. As
should be appreciated from a review of the following description, the
attenuation assembly of the present invention greatly improves the
performance and reliability of the compressor 10 by attenuating the gas
pressure pulsations at discharge outlet port 14.
As is known in the art and shown, for example, in U.S. Pat. No. 4,815,358
to Smith, issued Mar. 28, 1989 (assigned to the assignee of the present
invention), the variable angle wobble plate compressor 10 is formed
primarily by the combination of a cylinder block 16, a compressor head 17
and a crankcase 19. The cylinder block 16 includes five axially aligned
cylinder bores 18 (only one is shown in FIG. 1). A piston 20 is slidingly
engaged for reciprocal motion within each of the cylinder bores 18. The
reciprocating action of the piston 20 is utilized to compress and
circulate refrigerant fluid throughout the air conditioning system. The
compressed refrigerant gas is discharged from the outlet port 14 of the
compressor 10 where it is utilized by the air conditioning system to
condition air being directed to the vehicle interior. The "spent" or low
pressure refrigerant gas is then returned to the compressor 10 through an
inlet port (not shown) to complete the cycle.
A central drive shaft 22 is axially aligned within the cylinder block 18
and crankcase 19. The drive shaft 22 extends externally from the crank
case 19 and is attached through an electromagnetic clutch 24 to a pulley
26. A fan belt (not shown) is attached to the pulley 26 and to the vehicle
engine (not shown). During engine operation, the fan belt transmits power
from the engine to the pulley 26 and the drive shaft 22 to the compressor
10. A journal plate assembly 28 is provided for reciprocating the pistons
20. The journal plate assembly 28 includes a rotary driving plate 30 that
is attached to a driving lug 32 connected to the drive shaft 22. In this
way, the driving plate 30 is rotated with the drive shaft 22.
The driving plate 30 includes a journal 34 on which a non-rotary wobble
plate 36 is mounted. The wobble plate 36 is prevented from rotating by its
connection to a stationary guide rod 38. More specifically, the non-rotary
wobble plate 36 is mounted at its inner diameter on the journal 34 and is
axially retained thereon against a needle bearing 40. A more in-depth
understanding of this configuration is disclosed in U.S. patent to Smith
U.S. Pat. No. 4,815,358, mentioned above.
As the drive shaft 22 rotates, the driving plate 30 is rotated therewith,
through its connection with the drive lug 32. This in turn imparts a
nutating motion to the non-rotary wobble plate 36. The precise path of the
wobble plate 36 is determined by the angle of the journal plate assembly
28 to the drive shaft 22. More particularly, when the journal plate
assembly 28 is positioned at a maximum angle as shown in FIG. 1, the
nutating motion is at a maximum. Thus, through the connection of the
pistons 20 to the wobble plate 36 by means of the piston rod 42, it should
be appreciated that the pistons are then reciprocated through their full
stroke. Accordingly, the compressor 10 operates at maximum capacity.
Conversely, when the journal plate assembly 28 is adjusted so as to be
perpendicular to the drive shaft 22, the driving plate 30 spins freely
without imparting motion to either the wobble plate 36 or the pistons 20.
The operation of the compressor 10 is effectively terminated in this
position. Of course, by varying the angle of the journal plate assembly 28
anywhere between these two extremes, an infinite number of intermediate
capacity levels may be achieved by the compressor 10.
Refrigerant gas is introduced into the compressor 10 through an inlet port
(not shown) and delivered into an annular suction cavity 44 located within
the compressor head 17. Inlet reed valves 45 (FIG. 2) are provided for
each cylinder 18 on valve plate 48. During the piston intake stroke,
sufficient suction force is generated by the piston 20 to open each valve
45 in sequence and draw refrigerant fluid from the suction cavity 44 into
the corresponding cylinder bore 18. During the discharge stroke, the
refrigerant gas is compressed within the cylinder bore 18 causing a
discharge reed valve 50 to snap open (see FIG. 1), whereby the high
pressure refrigerant gas is expulsed from the cylinder bore 18 into
discharge chamber 52. The inlet and discharge reed valves 45, 50 provide
for unidirectional fluid flow through the compressor 10, and ultimately
assure proper fluid circulation throughout the air conditioning system.
In typical compressor systems, fluid is freely discharged from the
discharge chamber 52 through the outlet port 14. As discussed previously,
this results in pressure pulsations evidenced throughout the system
coinciding with the discharge stroke of the pistons 20. The present
invention provides an assembly in the form of a valving means that
regulates the volumetric output of the refrigerant fluid from the outlet
port 14, thereby greatly attenuating these pressure pulsations.
A key component of the valving means is a timing plate 12 mounted for
rotary movement in the compressor discharge chamber 52. The timing plate
12 is circular and centrally attached to the end of the drive shaft 22,
whereby rotation of the drive shaft imparts the desired synchronized
rotation. The timing plate 12 is placed in proximate location to the end
wall of the compressor head 17, such that only a small gap or clearance is
provided. The significance of this clearance is discussed in more detail
below.
As shown in FIG. 3, the timing plate 12 includes a plurality of flow
orifices 54. The orifices 54 are uniformly spaced about a constant annular
radius from the central axis of the timing plate 12. The flow orifices 54
are preferably pearshaped and oriented such that a narrow end of the flow
orifice 54 leads a wide end as the timing plate 12 rotates. This variable
shape, in combination with the rotation of the timing plate 12, serves to
effectively vary the flow-through area of the valving means to the outlet
port 14, so as to minimize discharge pressure pulsations therefrom. The
radius, or distance of the orifices 54 from the central axis of the timing
plate 12, is provided such that the orifices 54 align with the outlet port
14 during rotation of the timing plate 12.
The timing plate 12 rotates such that each orifice 54 periodically aligns
with the compressor outlet port 14. As the narrow end of each orifice 54
comes into alignment with the outlet port 14, there is a gradual opening
of the flow-through area. As the pressure is lowered, the flow-through
area progressively increases. As previously discussed, by providing only a
small exit opening when the pressure within the discharge chamber is high
and a gradually larger opening when the pressure within the discharge
chamber 52 is being decreased, an essentially constant volumetric rate of
fluid can be discharged from the discharge chamber 52.
To review the entire sequence, FIG. 1 shows the operation of the present
invention at a point in time when the piston 20 is in a discharge stroke.
The discharge reed valve 50 is open as the refrigerant gas is discharged
from the cylinder bore 18 into the discharge chamber 52. At this point of
high discharge pressure, a solid portion or face of the timing plate 12 is
coincident with the outlet port 14. Only restricted flow through the flow
ring around the gap between lip 51 of outlet port 14 and the plate is
possible. It should be appreciated from the above discussion that a narrow
end of one of the flow orifices 54 is about to rotate into alignment with
the outlet port 14. When this does happen, compressed refrigerant gas
within the discharge chamber 52 then begins discharging through the
uncovered small opening, as well as continuing around the flow ring.
FIG. 2 shows the operation of the compressor 10 at a point in the cycle
when the pressure in the chamber 52 is dissipated and is now relatively
low. At this time, the piston 20, illustrated in the drawings, happens to
be on the intake stroke. The discharge reed valve 50 is closed, preventing
gas from escaping from the discharge chamber 52 back into the cylinder
bore 18. The flow orifice 54 completes the movement across the outlet port
14 so that it is in a position with the wide end aligned over said port
14, thereby providing the maximum flow-through area. It should be
appreciated that, by this point in the cycle, the pressure within the
discharge chamber 52 is sufficiently diminished such that the increased
flow area effectively serves to offset the decreased chamber pressure. In
effect, this continues to provide an essentially constant volumetric fluid
discharge from the outlet port 14. The result is a corresponding constant
depressurization and elimination of pressure spiking in the chamber 52,
and thus within the refrigerant line outside the compressor 10.
The gap between the lip 51 and the timing plate 12 is important. First, the
gap is necessary so that, at the times when a solid portion of the timing
plate 12 covers, or is aligned with the outlet port 14, fluid continues to
discharge in a controlled manner. Otherwise, the pressure in the chamber
52 and the outside refrigerant line attached to the port 14 would build
up. Indeed, the pulsing effect would be exaggerated unless flow through
this limited, restricted gap forming the flow ring can thus be maintained.
Secondly, the closely spaced lip 51/timing plate 12 configuration also
enhances the pulsation cancellation effects. This is effective over the
full range of pressures and helps dissipate the staggered discharge pulses
coming from the different cylinder bores 18. More particularly,
pressurized refrigerant gas enters the discharge chamber in a
directionalized fashion as it is discharged from the cylinder bores 18.
Each pulsation is initially partially diminished by interception at an
angle of incidence with the out of phase pulsations from the other
cylinder bores 18. Especially during the time when a solid portion of the
timing plate 12 aligns and covers the outlet port 14, the pulsations are
further reduced by being reflected back and forth between the timing plate
12 and the back wall of the compressor head 17. The plate 12 is also
constantly rotating, so that the boundary layer effect causes additional
multidirectional flow vectors to help intercept and cancel the pulsing
flow. Finally the high energy flow ring generates additional opposite and
angular vectors, thereby further attenuating the pulsations.
Advantageously, the relative lengths of the orifice 54 and adjacent solid
portion of the disc 12, as well as the relative size and shape of the
orifice 54 and the outlet port 14, can be varied to effectively tune the
attenuation assembly of the compressor 10. This helps achieve maximum
pulsation attenuation.
As previously described, the flow orifice 54 first begins to align with the
outlet port 14 after the piston 20 completes its discharge stroke.
Likewise, the increasingly larger area of the orifice 54 is aligned with
the outlet port 14 as the pressure subsides in the chamber 52. So that the
pulse from each cylinder 18 is fully attenuated, in the preferred
embodiment, the number of orifices 54 provided in the timing plate 12 is
equal to the number of the cylinders 18.
Consistent with the concepts and teachings of the present invention, it
should be appreciated that an alternate embodiment of the attenuation
assembly may employ a timing plate advancing and retarding mechanism. That
is, it may be desirable to incorporate a mechanism to actively advance or
retard the orientation of the timing plate 12 depending upon the variable
speed of the compressor 10 a driven through the clutch 24. This would
effectively further assure proper positioning of the timing plate 12 to
thereby provide improved pulsation attenuation.
In summary, various benefits and advantages are realized by the pressure
pulsation attenuation assembly of the present invention. Among these
advantages are smoother and quieter system operation and enhanced
compressor 10 reliability. These benefits combine to result in a vehicle
providing improved quality, performance and, correspondingly, increased
customer satisfaction.
The foregoing description of a preferred embodiment of the invention has
been presented for purposes of illustration and description. It is not
intended to be exhaustive or to limit the invention to the precise form
disclosed. Obvious modifications or variations are possible in light of
the above teachings. The embodiment was chosen and described to provide
the best illustration of the principles of the invention and its practical
application to thereby enable one of ordinary skill in the art to utilize
the invention in various embodiments and with various modifications as is
suited to the particular use contemplated. All such modifications and
variations are within the scope of the invention as determined by the
appended claims when interpreted in accordance with breadth to which they
are fairly, legally and equitably entitled.
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