Expansible chamber devices – Relatively movable working members – Interconnected with common rotatable shaft
Reexamination Certificate
2001-10-12
2004-01-06
Look, Edward K. (Department: 3745)
Expansible chamber devices
Relatively movable working members
Interconnected with common rotatable shaft
C092S1650PR, C092S171100
Reexamination Certificate
active
06672199
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
The present application claims priority from German Patent Application No. 100 51 420.0, filed Oct. 17, 2000.
DESCRIPTION
The invention relates to a cylinder block of an axial piston compressor, in particular for use in a vehicle air conditioner employing CO
2
as coolant.
The air conditioners installed in motor vehicles employ coolant compressors of various constructions. In recent years, however, so-called axial piston compressors have become predominant.
FIG. 4
shows this kind of axial piston compressor according to the state of the art, in diagrammatic longitudinal section. This is a so-called swash-plate compressor to be used with R134a as the coolant. A compressor shaft
1
is driven by way of a pulley associated with a magnetic coupling
2
. A swash plate
3
is coupled to the drive shaft
1
. The swash plate
3
is fixedly attached to the drive shaft
1
and rotates therewith. Various forms of linkage are known for mounting and centering the swash plate
3
on the drive shaft
1
in such a way that although the plate cannot rotate with respect to the shaft, it is possible for the axis
3
a
of the swash plate
3
to be tilted relative to the axis
1
a
of the drive shaft
1
. The tilt angle of the swash plate
3
as a rule is limited to a minimal (
3
b
) and a maximal (
3
c
) value by two stopping devices. Customarily one or two guide pins
4
are needed so that the tilting movement can be carried out in a specified manner, with no risk of the plate becoming jammed during the adjustment. The means of limiting the tilting movement, i.e. the limit stops, can also be integrated into the region of the guide pins
4
. In the example shown in
FIG. 4
, the guide pin is fixedly attached to the swash plate
3
and incorporates a bearing
5
a
that is movable with respect to a stopping plate
5
and that is responsible for centering the guide pin (see reference numeral
4
a
in FIG.
4
). The stopping plate
5
, which is likewise attached to the shaft, is supported by way of an axial bearing
6
.
The swash plate is not only adjustable regarding its angle with respect to the drive shaft
1
, but can also be shifted axially along the drive shaft
1
. This shifting is necessary so that the top-dead-center point of the associated piston
8
can be maintained despite differences in the plate angle. Ordinarily limit stops are provided that prevent the swash plate
3
from being displaced beyond an upper seating
3
d
and a lower seating
3
e
on the drive shaft
1
. The displacement mechanism is pretensioned to a specified degree by a compression spring
7
. The stroke of the piston is determined by the tilt angle of the swash plate
3
. When this angle is as large as possible, the stroke is maximal; a minimal tilt angle results in a minimal piston stroke.
The pistons
8
in the embodiment illustrated here are connected to the swash plate
3
by way of hemispherical linkage elements
9
,
10
. To absorb the tensile-pressure load, above a piston one linkage element
10
is disposed on the lower bearing surface
3
g
of the swash plate
3
and another linkage element
9
is disposed on its upper bearing surface
3
f
. By way of their flat surfaces
9
a
,
10
a
, the linkage elements run over complementary bearing surfaces of the swash plate
3
at the full circumferential velocity with a radial movement superimposed, with the result that the path of the linkage elements on the swash plate is elliptical. The convex upper surfaces
9
b
,
10
b
of the linkage elements are seated in indentations in the piston
8
that have a complementary, hemispherical form; while the compressor is in operation, there is a comparatively small amount of relative movement here. The axial piston compressors described above comprise several pistons distributed about their periphery, customarily three to eight pistons.
FIG. 9
shows a side view of a piston
8
such as is employed in an axial piston compressor like that shown in FIG.
4
. The piston
8
consists of two sections, namely a piston shaft
8
a
and a piston neck
8
b
. The term “shaft” is used here to designate the part or section of the piston that is disposed within an associated cylinder bore which guides its back-and-forth it movement. The piston neck
8
b
, which customarily comprises a U-shaped cavity
8
c
, encloses the above-mentioned swash plate
3
and, in combination with the linkage elements
9
,
10
, serves to transmit the forces from the swash plate
3
to the piston shaft
8
a
. The back surface of the piston neck
8
b
is in contact with the inner surface of the drive-mechanism housing, in such a way that as the piston
8
moves back and forth, it is prevented from rotating within the associated cylinder bore.
FIG. 7
shows a specific way in which this rotational stability is accomplished. Supplementary information is provided in the document EP 0 740 076 A2. In order to limit the rotation of the piston
8
about its long axis, on the side of the piston neck that faces the drive-mechanism housing a convex surface
72
is disposed. Opposite to and spaced somewhat away from this surface is a concave surface in the housing
71
. The radius R
1
of the convex surface
72
is larger than the radius R
p
of the cylindrical outer surface of the piston shaft, but smaller than the radius R
2
of the concave inner surface in the housing
71
. The contact between the convex surface
72
and the concave surface of the housing
71
limits the extent to which the piston
8
can rotate about its long axis. The dashed line shows that if the piston
8
rotates, only one edge
74
of the convex surface
72
touches the concave inner surface of the housing
71
. To reduce friction and avoid wear and tear, it is advisable to treat the surfaces appropriately.
In
FIG. 8
an alternative means of guiding the piston longitudinally is illustrated. This alternative construction to prevent unintended rotation of the piston
8
comprises a ridge
82
disposed along the piston shaft, which engages with a corresponding groove
83
in the face of the cylinder bore
81
.
The translational movement of the piston
8
in the associated cylinder bore requires the dimensions, shape, position and surface properties of the parts and/or surfaces that correspond to one another to be very close to specifications.
FIGS. 4
,
7
,
8
and
9
document the classical state of the art insofar as it pertains to the axial piston compressor for a vehicle air conditioner. When R134a is used as the coolant, the piston diameter is about 30 mm. Because CO
2
is a distinctly higher-performance coolant, compressers employing CO
2
can have a considerably smaller stroke volume. On the other hand, it is necessary to cope with comparatively large pressure differences. That is, when CO
2
is used as the coolant, the pressures exerted on the piston
8
are considerably greater. To compensate for these higher pressures, CO
2
compressors are provided with pistons of considerably smaller diameter, e.g. about 16 mm.
However, as is illustrated in
FIG. 5
, when the shaft of a piston has such a small diameter, its neck projects further outward; that is, it is displaced to the side with respect to the long axis of the piston. In the embodiment shown in
FIG. 5
the pistons
8
are driven by a wobble plate
29
. The wobble plate
29
rests against a swash plate
33
by way of antifriction bearings
30
,
28
and
24
. By means of an internally threaded fixation disk
31
, the wobble plate is fixed so that its axis coincides with that of the swash plate. The pistons are coupled to the wobble plate by way of linkage bearings
27
and
25
and by a set screw
26
. The piston
8
consists of a shaft
8
a
and a neck
8
b
. These are separated by a transitional region
8
c
, which connects the shaft to the neck. In the case of an R134a compressor this transitional region is not necessary, because (as shown in
FIG. 9
) the neck of the piston has a diameter no greater than that of the associated shaft. The pistons
8
shown in
FIG. 5
are guided axially in their b
Andrus Sceales Starke & Sawall LLP
Lazo Thomas E.
Look Edward K.
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