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Description  |
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BACKGROUND OF THE INVENTION
The invention relates to a supply unit for fluids. Supply units for fluids,
such as the roller cell pumps which are frequently used for supplying fuel
under pressure, are known in a variety of types. As in FIG. 1, which shows
the known prior art illustrated in schematic fashion, such pumps include a
rotor disc or grooved disc 1 having reception grooves 2 distributed about
its circumference in which are located positive-displacement bodies 3.
These bodies 3 may be formed as rollers, which are guided and slide in the
grooves 2 and which contact an external roller path 4; the path 4 is of
circular shape like the circumference of the grooved disc 1 but is,
however, eccentrically shifted by a certain given distance at its center,
so that crescent-shaped pumping work chambers are created which travel
about the circumference of the system and supply the induced fluid, such
as fuel, to an external groove 13 and, via the play between the roller and
reception element to an internal pressure groove 10 while the fluid to be
supplied or the rotor disc 1 rotates along the arrow A in its eccentric
displacement with respect to roller path 4. Because of the eccentricity, a
widest gap WS between the roller path 4 and the jacket surface of the
rotor and a narrowest gap ES result, which gaps naturally are periodically
traversed by the rollers 3 in their grooves upon the rotation of the
driven rotor.
In order to understand the present invention, it is necessary also to
explain the functional sequence of a known roller cell pump to a certain
extent, with the aid of FIGS. 2a through 2c and FIGS. 3a through 3e and
the individual working phases represented thereby in order, thus, to
clarify the disadvantages inherent therein.
In FIG. 1, the following references are also given, which appear as well in
the working phases of FIGS. 2 and 3. V.sub.1 and V.sub.2 indicate,
respectively, the chamber under roller 3.sub.1 and 3.sub.2 ; the
crescent-shaped chamber between rollers 3.sub.1 and 3.sub.2 and that
between rollers 3.sub.2 and 3.sub.3 are designated V.sub.3 and V.sub.5,
respectively. The pressure side, extending in each case from the uppermost
roller which has passed with widest gap WS, toward the bottom on the
left-hand side of the system shown in FIG. 1, is marked D, and the intake
side is marked S.
First, the buildup of pressure at the widest gap WS will be described in
various working phases with the aid of FIGS. 2a through 2c; for the sake
of simplification, a supply medium free of bubbles, such as fuel, is
assumed. In FIG. 2a, the roller 3.sub.1 separates the intake chamber S, in
which intake pressure prevails, from the chamber V.sub.1 under the roller
3.sub.1 and from the crescent-shaped chamber V.sub.3 between the rollers
3.sub.1 and 3.sub.2. A buildup of pressure has not yet occurred in
chambers V.sub.1 and V.sub.3 ; thus, intake pressure also prevails in
chambers V.sub.1 and V.sub.3. The forwardmost edge 8 of the chamber
V.sub.1 has not yet reached the overlap area of the protruding chamber
portion 9 of the internal pressure groove 10, in which, as in the pressure
chamber 11 and the crescent-shaped chamber V.sub.5 located in front of the
roller 3.sub.2, operational pressure prevails. The distance of the forward
edge 8 from the protruding area 9 of the pressure groove 10 amounts to
approximately 10.degree., as shown.
Within the next 3.degree., that is, at a distance of 7.degree. between the
two parts 8 and 9, a substantial pressure buildup (compression) results in
the closed chamber comprising V.sub.1 and V.sub.3, as a result of the
reduction in volume of chamber V.sub.3 (FIG. 2b). Within these 3.degree.,
a substantial pressure peak of over 10 bar can occur in this chamber
V.sub.1 plus V.sub.3, as a result of which, roller 3.sub.2 lifts from its
previous contact at the rearward groove edge (as seen in the direction of
rotation. As a result, there is a connection of the crescent-shaped
chamber V.sub.3 and chamber V.sub.1 with the pressure chamber over the
area through which the arrow B extends. The chamber V.sub.1 under the
roller 3.sub.1 is, as may be seen, not yet directly connected with the
pressure groove 10.
Only in the working phase shown in FIG. 2c are both the crescent-shaped
chamber V.sub.3 and the chamber V.sub.1 first connected with the pressure
chamber 11 via the pressure groove 10, whereby the fluid, displaced out of
the chamber V.sub.3, flows past the rollers 3.sub.1 and 3.sub.2 into the
pressure chamber in accordance with arrows B and B'.
The working phases shown in FIGS. 3a through 3e show the pressure
conditions and the sealing at the narrowest gap ES with pumping bodies or
rollers 3.sub.1, 3.sub.2 and 3.sub.3, in the meantime, having traveled
farther in the rotary direction. As may be seen, the intake chamber or
intake spheroid 12 extends nearly to the narrowest gap ES and, in the
working phase shown in FIG. 3a, is already connected with the chamber
located in the area of roller 3.sub.3. At this point, the crescent-shaped
chamber V.sub.3 is connected as indicated by arrow C with an external
pressure groove 13 whereby the fluid displaced out of the crescent-shaped
chamber V.sub.3 flows via the external pressure groove 13 and, according
to arrow E, past the roller 3.sub.2 via the inner pressure groove 10 into
the pressure chamber 11. The gap width at the narrowest gap ES determines
the leakage quantity overflowing out of the crescent-shaped chamber
V.sub.5 formed between rollers 3.sub.3 and 3.sub.2 and into the intake
chamber. In the crescent-shaped chamber V.sub.5, operational pressure
prevails.
In the working phase of FIG. 3b, the connection from chamber V.sub.2 under
roller 3.sub.2 via the inner pressure groove 10 to the pressure chamber 11
is interrupted, for the groove bottom area 14 at that point is just
leaving the inner pressure groove 10. The fluid displaced out of chamber
V.sub.2 and the crescent-shaped chamber V.sub.3, which is becoming
narrower and narrower, flows via the external pressure groove 13 according
to arrow F into the pressure chamber, whereby chamber V.sub.5 is still
connected via the external pressure groove 13 with the pressure chamber
and a leakage quantity continues to overflow into the intake chamber area.
Only in the working phase of FIG. 3c is the chamber V.sub.5 first separated
by the roller 3.sub.2 from the external pressure groove 13 whereby the
pressure in chamber V.sub.5 rapidly drops as a result of the quantity of
overflow across the narrowest gap ES. Roller 3.sub.2 is pressed by the
operational pressure in chamber V.sub.2 and the crescent-shaped chamber
V.sub.3 against the forward groove edge, as shown at reference numeral 15,
and thus seals off chambers V.sub.2 and V.sub.3 from chamber V.sub.5. From
this moment, the leakage quantity at the narrowest gap is no longer
determined by the gap width of distance but rather by the remaining volume
of chamber V.sub.5 whereby the fluid, further displaced out of chambers
V.sub.2 and V.sub.3, flows via the external pressure groove 13 into the
pressure chamber 11. Between groove 13 and chamber 11, there is a
connection which is not shown.
In the working phase of the parts in FIG. 3d, the roller 3.sub.2 seals off
chambers V.sub.2 and V.sub.3 from the intake chamber at the narrowest gap,
because the roller 3.sub.2 continues in contact with the forward groove
edge. From this point on, the chamber V.sub.2 under the roller 3.sub.2
becomes larger, because the roller 3.sub.2, with the roller path growing
increasingly distant from the rotor, moves farther and farther out of its
groove. Simultaneously, the gap 16 between the rear groove edge and the
roller path grows smaller and smaller and finally reaches the gap distance
established by the narrowest gap ES.
The operational pressure available in chamber V.sub.2 then drops as well,
when the quantity flowing from chamber V.sub.3 toward chamber V.sub.2 is
smaller than the volumetric increase of chamber V.sub.2 resulting from the
further rotation of the rotor.
In the working phase of the parts as shown in FIG. 3e, the rear groove edge
is at the narrowest gap ES and the gap between groove edge 17 and roller
path has reached the minimum. As seen on the leakage quantity flowing
through the narrowest gap ES is smaller than the volumetric enlargement of
chamber V.sub.2, the roller 3.sub.2 lifts from the forward groove edge at
18 and the pressure in chamber V.sub.2 drops practically at once to the
lesser intake pressure, or below. The difference between the particular
groove volume and the roller volume each time a roller traverses the
narrowest gap ES is the so-called clearance volume, which is reduced upon
traversal of the narrowest gap ES from the operational pressure to the
intake pressure.
In such a supply pump for fluids having an eccentric, circular roller path,
difficulties arise which may be quite substantial as a result of the lack
of sealing at the narrowest gap and as a result of unfavorable expansion
and compression relationships after the narrowest gap ES and before the
widest radial gap WS, particularly (with respect to a fuel supply pump)
during so-called hot-gasoline operation.
Since the sealing point between the pressure chamber D and the intake
chamber S is formed only by a jacket line having the desired radial play
(ES) of a few .mu.m and, as explained above, the distance between the
rotor and the roller path rapidly increases with increasing distance from
the narrowest gap ES, a large quantity of fuel can flow back from the
pressure side to the intake side and there cause functional interruptions
as a result of volatilization, particularly during hot-gasoline operation.
The beginning of the intake spheroid 12 must also not be brought too close
to the narrowest gap ES, because otherwise a direct connection could
result between the pressure side and the intake side as a result of a
shortcut via the roller groove in the rotor disc. However, this has the
result that, after the narrowest gap, there is an expansion of the sealed
chamber volume which, until the intake spheroid is opened, that is, until
the intake spheroid 12 is reached, can cause significant underpressures,
so that the return flow of fuel and its volatilization are still further
encouraged.
Furthermore, at the closing of the intake spheroid 12 before the widest gap
WS (see FIGS. 2a-2c), that is, when a particular roller area leaves the
intake spheroid area, a compression phase has already occurred for the
external partial chamber volume between the rotor and the roller path,
while, in contrast, the inner partial chamber volume in the roller groove
enlarges still further, which can also have undesirable effects.
There is accordingly a need for a supply unit for fluids whose basic
concept corresponds to a roller cell or vane cell pump and in which the
disadvantages of the known eccentric circular roller path which are
described above are avoided, that is, in which the sealing effect of the
radial gap is increased and the expansion and compression phases are
adapted to the opening and closing conditions of the intake and pressure
spheroids.
OBJECT AND SUMMARY OF THE INVENTION
The supply unit for fluids constructed in accordance with the invention has
the advantage over the prior art in that the radial play between the
roller path and the grooved disc which is adjustable by means of
displacement of the intermediate plate which forms the roller path in an
interior bore--that is, generally stated, the radial play which is
adjustable by means of a relative displacement between the intermediate
plate and the rotor or grooved disc--can be kept approximately constant
over a large angular range before and after the narrowest gap in the form
of the roller path in accordance with the invention, in fact, over a range
of approximately .+-.20.degree. before and after the narrowest gap. This
permits the attainment of a substantially better sealing effect compared
with that in an eccentric, circular roller path in which the radial play
progressively increases with the distance from the narrowest gap.
By means of the transition of the roller path approximating a circular
contour concentric with the center of the rotor or grooved disc, the
compression phase of the pumping chamber can be terminated quite a
distance before the narrowest gap. The closing of the pressure groove can
then occur earlier, whereby, in an analogous manner the expansion of the
particular pumping chamber is initiated later after the narrowest gap and
therefore the intake groove can, accordingly, be opened later.
It is particularly advantageous that the very marked underpressure
formation which results from the expansion of the chamber volume after the
narrowest gap before the intake groove is opened can, to a great extent,
be avoided.
At the widest gap, that is, at the transition from the intake to the
pressure side, the approximately circular path of the roller path, which
is also concentric with the center of the rotor, means that the intake
spheroid can be closed at such a time when both the exterior partial
chamber volume and that volume located under the roller have both already
terminated their expansion phase. As a result, the course over time of the
compression in the region of the negative overlap (that is, when the
crescent-shaped chamber V.sub.3 and chamber V.sub.1 under the roller are
connected neither to the pressure side nor the intake side) can be
accomplished with a more gradual transition.
In addition, a more gradual process of compression results as the pump
continues to rotate further.
The previously referred to relatively high pressure peaks resulting from
compression of the fluid in the chamber volume which is entirely closed
off at a rotary angle of 10.degree. (see FIGS. 2a-2c) may be entirely
prevented by means of an appropriate positioning of the control edges;
that is, this 10.degree. range is so located that it coincides with the
angular range in which no compression, or an extremely limited amount of
compression, takes place. In addition, this can result in a reduction in
noise, because the severe pressure fluctuations which permit a fluctuation
of the supply medium are reduced.
In addition, with particular reference to a roller cell pump, there is an
additional protection against pressure peaks, even when the peaks have
already been reduced to a certain extent automatically by means of
appropriate roller movements.
In vane cell pumps, where such a self-regulating function is not present
and where previously such pressure peaks could be reduced only via
compression oil grooves or bores, this effect of a "braked" compression
signifies a decisive improvement.
It is particularly advantageous that the requirement for a concentric,
approximately circular course of the roller path about the center of the
grooved disc or rotor can be very well accomplished in that the roller
path can be composed of two ellipse halves. Then the elliptical shape can
almost exactly be obtained in the area of the apex points which
approximate primary circles of curvature.
The invention can be realized without comparatively great expense because
the centers of the two ellipse halves are identical and, furthermore, the
rotor center is not identical with the centers of the particular primary
circles of curvature of the ellipses.
The invention will be better understood as well as further objects and
advantages thereof become more apparent from the ensuing detailed
description of the preferred embodiment taken in conjunction with the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of a well-known roller cell pump;
FIG. 2a is a schematic illustration similar to FIG. 1 of a portion of a
well-known roller cell pump relating to the function and pressure buildup
at the widest gap in a first working phase;
FIG. 2b is a view similar to FIG. 2a of a second working phase of a
well-known roller cell pump;
FIG. 2c is a view similar to FIG. 2a of a third working phase of a
well-known roller cell pump;
FIG. 3a is a schematic illustration of the lower portion of the roller cell
pump of FIG. 1 illustrating the pressure conditions and the sealings at
the narrowest gap in a first working phase;
FIG. 3b is a view similar to FIG. 3a showing the parts in a second working
phase;
FIG. 3c is a schematic illustration similar to FIG. 3a showing a third
working phase of the parts;
FIG. 3d is a schematic illustration similar to FIG. 3a showing the parts in
a fourth working phase;
FIG. 3e is a schematic illustration similar to FIG. 3a showing the parts in
a fifth working phase; and
FIG. 4 is a schematic showing of the roller path for the supply pump of the
invention operating on the basic principle of a roller piston pump in
which the rollers follow a pump inner chamber having a non-circular
contour.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The basic concept of the present invention is to improve the operation of
fluid supply pumps, particularly during hot operation of the medium to be
supplied, i.e., in a fuel supply pump, during hot-gasoline operation. By
means of a new embodiment of the roller path disposed eccentrically
relative to the rotor, with the roller path being so formed that it is
virtually, and, from the practical standpoint, approximates a circular
course which extends, in a certain angular range about the narrowest and
the widest gap, concentrically about the rotor center; that is, about the
center of the grooved disc or rotor disc which receives the pumping bodies
or rollers in grooves.
As shown in FIG. 4, the rotor or grooved disc center point is indicated at
M. From this center M, the radius R.sub.2 of the rotor extends which, in
rotating about the center M, defines the jacket line of the grooved disc
which is shown in broken lines in FIG. 4 and indicated by the reference
numeral 20.
In the known circular roller cell pump, there is a center point M',
disposed at a distance e.sub.kr and thus eccentrically with respect to the
center M of the eccentric circular contour of the known roller path 21
having the radius R.sub.1, which path 21 extends as a circle about the
center M' and is depicted in FIG. 4 by a fine line.
The invention departs from the above described arrangement in that in order
to form the roller path in accordance with the invention, which is shown
in FIG. 4 and depicted by a heavy line and identified by the reference
numeral 22, the roller path is divided into two halves, an upper half 22a,
which comprises somewhat less than a "semicircle" and at 23 and 24 turns
into a lower half 22b, which is somewhat larger than a "semicircle". The
upper and lower halves 22a, 22b formed respectively by radius vectors
.rho..sub.1 (.phi.) (referring to the upper half 22a) and .rho..sub.2
(.phi.) (referring to the lower half 22b) extending about the center M of
the grooved disc, the length of these radius vectors being a function of
the angle .phi..
In the illustrated embodiment, the ellipse halves 22a and 22b form the
roller path for the rollers of the rotor of the pump, which, placed
together with transition points at 23 and 24, form the roller path in
accordance with the invention. Because the ellipse shape can be virtually
exactly approximated in the area of the apex points WS and ES by means of
their primary circles of curvature which follow the curvature of a circle
in the area of WS and ES as shown by the thin line circle 21 having a
center M', this embodiment of a roller path in accordance with the
invention fulfills extraordinarily well the basic concept of the present
invention as it has been defined above namely, within a certain angular
range about the narrowest and widest gap to be approximately identical
with a concentric circle about the rotor center. The narrowest gap is
shown between the rotor and the roller path at ES and the widest gap is
shown between the rotor and the roller path at WS.
The centers of the two ellipse halves are identical and in FIG. 4 are
designated M.sub.e. The rotor center M is identical with the centers of
respective circles of curvature which centers at M which practically
identically represent the ellipse shape in the area of the apex points WS
and ES. That is, a circular arc with radius R2 will substantially coincide
with the ellipse 22b beginning on opposite sides of ES and a circular arc
with radius R2+S2 will substantially coincide with ellipse 22a beginning
on opposite sides of WS.
In other words, based on the foregoing it will be understood that in this
structure the roller path formed by the two elliptical halves, having the
same geometrical center Me disposed eccentrically to the grooved disc 20
for contact by the rollers is arranged so that the ellipse shape about the
apex points WS and ES of the ellipse halves represent approximate circular
arcs.
There is a distance S.sub.2 between the ellipse center M.sub.e and the
rotor center M which is produced by the need for sufficient overlapping of
the groove edge with the roller jacket line contacting it.
As seen in FIG. 4 a roller vane pump is formed with an internal casing
surface 22 formed by two ellipse halves 22a and 22b having a geometrical
center Me and joined at their ends 23 and 24. The transition from one
ellipse half to the next ellipse half has a relatively smooth transition
at their joints 23 and 24 because the surfaces so formed are substantially
circular arc sections as shown by the circle 21 which coincides with the
ellipse halves at 23 and 24 and at the apex ends of the ellipse halves at
WS and ES. The smooth roller path formed by the ellipse halves defines a
contact surface for the peripheral rollers of the rotor having a center M.
The rotor axis is mounted off center from the center of the roller path so
that the narrowest point between the rotor and the roller path is at ES
and the widest point between the rotor and the roller path is at WS. As
seen from the drawing, the rotor center M is not the same as the centers
Me of the ellipse halves. The geometric center Me of the two ellipse
halves are not identical with the center point M of the rotor. The path
formed by the ellipse halves are ellipital with respect to their
geometrical centers Me; however, the elliptical path approximates a
circular arc along the portion at WS and ES with radii coinciding with the
center M of the rotor. Therefore, the ellipse halves approximate a
circular arc with respect to the center of the rotor disc when their
centers coincide with the center M of the rotor.
The major semi-axis a.sub.1 of the upper ellipse half is identical to the
minor semi-axis b.sub.2 of the lower ellipse half. The constant radius of
the primary circle of curvature of the lower ellipse half 22b at ES
corresponds to the constant radius R.sub.2 of the rotor disc. For the
upper half 22a, the radius of the circle of curvature is equal to the
rotor radius R.sub.2 plus the center point displacement S.sub.2 at WS.
This can be easily seen with the aid of the following equations for the
roller path, expressed in polar coordinates. For the radius .rho..sub.1
dependent on the angle .phi. and therefore variable, the following
equation results:
##EQU1##
where .rho..sub.1 lies between the limits of
##EQU2##
The equation for the lower path or ellipse half 22b results in:
##EQU3##
where .rho..sub.2 lies between the limits of
##EQU4##
The two radii .rho..sub.1 and .rho..sub.2 dependent on the angle .phi. are
each identical at the transition points 23 and 24, as can readily be
ascertained by inserting numerical values into the two equations (1) and
(2), so that a roller path results having a continuous transition.
The following Table I shows the calculated radii, varying in accordance
with the angle .phi., of both roller path halves 22a, 22b as an embodiment
of the invention although it should be understood that the invention is,
of course, not limited to this. The calculated values, however,
demonstrate particularly well the advantages which result in the practical
operation of a roller cell pump or a comparable unit on the basis of the
roller path in accordance with the invention.
The following values are the basis for the calculation:
R.sub.2 =15 mm
S.sub.2 =2 mm
while in FIG. 4, on the same scale, R.sub.1 has a value of 16 mm and the
eccentric distance e.sub.kr amounts to 1 mm.
TABLE I
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1 2
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0.degree.
17.000 360.degree.
82.86 16.094
277.14
2 " 358 84 16.054
276
4 " 356 86 15.986
274
6 " 354 88 15.921
272
8 " 352 90 15.858
270
10 17.000 350 92 15.797
268
12 16.999 348 94 15.740
266
14 16.999 346 96 15.684
264
16 16.998 344 98 15.632
262
18 16.997 342 100 15.581
260
20 16.996 340 102 15.534
258
22 16.994 338 104 15.489
256
24 16.991 336 106 15.446
254
26 16.988 334 108 15.406
252
28 16.984 332 110 15.368
250
30 16.979 330 112 15.332
248
32 16.973 328 114 15.299
246
34 16.966 326 116 15.268
244
36 16.958 324 118 15.239
242
38 16.948 322 120 15.213
240
40 16.936 320 122 15.188
230
42 16.923 318 124 15.166
236
44 16.908 316 126 15.145
234
46 16.891 314 128 15.126
232
48 16.872 312 130 15.109
230
50 16.850 310 132 15.094
228
52 16.826 308 134 15.080
226
54 16.800 306 136 15.068
224
56 16.771 304 138 15.057
222
58 16.739 302 140 15.047
220
60 16.704 300 142 15.039
218
62 16.667 298 144 15.032
216
64 16.626 296 146 15.025
214
66 16.582 294 148 15.020
212
68 16.536 292 150 15.016
210
70 16.486 290 152 15.012
208
72 16.433 288 154 15.009
206
74 16.377 286 156 15.007
204
76 16.318 284 158 15.005
202
78 16.256 282 160 15.003
200
80 16.191 280 162 15.002
198
82.86 16.094 277.14 164 15.001
196
166 15.000
194
168 " 192
170 " 190
172 " 188
174 " 186
176 " 184
178 " 182
180 15.000
180
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The dependence of the radius vectors .rho..sub.1 and .rho..sub.2 defining
the two different elipse halves on the angle .phi., at intervals of 2
degrees of angle at a time, may be drawn from the table, whereby at an
angle .phi.=82,86.degree., there is identity of radius vector .rho..sub.1
with radius vector .rho..sub.2. One moves therefore from the angle
82,86.degree. over from radius .rho..sub.1 to radius .rho..sub.2 and
allows the angle .phi..sub.2 for the lower ellipse half 22b to continue on
from 82,86.degree. up to 277.14.degree., corresponding to the transition
point 24, at which then the radius .rho..sub.2, having a numerical value
according to the table of 16.094, again turns into the radius .rho..sub.1
of the upper ellipse half.
From the table it can be seen that .rho..sub.1 is practically constant at
four points for an angle .phi..sub.1 =.+-.20.degree. in the area of
.phi..sub.1 =0. The same can be seen to occur for the numerical value of
15.00 for .rho..sub.2 in the range of 180.degree..+-.20.degree.. A course
of the roller path of this sort about the widest gap WS and the narrowest
gap ES is particularly advantageous, as a comparison of the circular
courses of rotor disc 20 and circular roller path contour 21 (broken and
fine lines; known embodiment forms) shows, which narrow sharply toward the
narrowest gap ES and widen out again thereafter, with the conditions which
make possible a virtual identity of the roller path according to the
invention already more than 20.degree. before the narrowest gap and more
than 20.degree. after the narrowest gap, with respect to the circular form
of the rotor disc.
In this area, before and after the narrowest gap ES (and analogously
applied to the widest gap WS), there is practically no noticeable volume
change any longer between the roller path and the grooved disc or rotor
jacket, so that here as well no volume displacements can arise which would
lead to extreme operating conditions. Still, the roller path in accordance
with the invention has practically the same volume-distance relationships,
albeit shifted, with the rotor disc, because what is missing, for example,
as a very small crescent-shaped chamber 25 in the third quadrant (first
forward half of the lower ellipse half 22b) appears as a supplementary
chamber 25' in the second quadrant, while the approach of the roller path
to the jacket surface of the rotor disc is greatest approximately in the
area of 26 and takes a substantially steeper course than in a known,
concentric circular roller path. However, this "compression phase" is
already terminated long before the narrowest gap; corresponding conditions
are found at all the critical transition areas described above, so that
the overall result in a substantially gentler, more gradual operation,
braked compression, and protection from pressure peaks as well as from the
increased wear and possible fluctuations which pressure peaks cause.
The foregoing relates to a preferred embodiment of the invention, it being
understood that other embodiments and variants thereof are possible within
the spirit and scope of the invention, the latter being defined by the
appended claims.
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