U.S. patent application number 16/328790 was filed with the patent office on 2019-07-11 for external gear pump for a waste heat recovery system.
The applicant listed for this patent is Robert Bosch GmbH. Invention is credited to Jakob Branczeisz, Guido Bredenfeld, Marc Laetzel, Matthias Riedle.
Application Number | 20190211819 16/328790 |
Document ID | / |
Family ID | 59152868 |
Filed Date | 2019-07-11 |
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United States Patent
Application |
20190211819 |
Kind Code |
A1 |
Bredenfeld; Guido ; et
al. |
July 11, 2019 |
EXTERNAL GEAR PUMP FOR A WASTE HEAT RECOVERY SYSTEM
Abstract
The invention relates to an external gear pump (1) having a pump
housing (2). An inlet (2a), an outlet (2b), and a working chamber
(6) are formed in the pump housing (2). A first gear (11), which is
arranged on a first shaft (21), and a second gear (12), which is
arranged on a second shaft (22), are arranged in the working
chamber (6) in such a way that said first and second gears mesh
with each other. Both gears (11, 12) have teeth having a tooth
width (b). The first shaft (21) is radially supported in at least
one plain bearing (61), and the second shaft (22) is radially
supported in at least one further plain bearing (63). The plain
bearing (61) has a bearing diameter (D63), and the further plain
bearing (63) has a further bearing diameter (D63). During operation
of the external gear pump (1), a delivery volume (V) of a working
medium can be conveyed from the inlet (2a) to the outlet (2b). The
two bearing diameters (D.sub.61, D.sub.63) are selected in such a
way that the ratio V/(D.sub.61.sup.2*b) is less than 1.1 and the
ratio V/(D.sub.63.sup.2*b) is less than 1.1.
Inventors: |
Bredenfeld; Guido;
(Markgroeningen, DE) ; Branczeisz; Jakob;
(Eberdingen, DE) ; Laetzel; Marc; (Stuttgart,
DE) ; Riedle; Matthias; (Obersulm, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Robert Bosch GmbH |
Stuttgart |
|
DE |
|
|
Family ID: |
59152868 |
Appl. No.: |
16/328790 |
Filed: |
June 20, 2017 |
PCT Filed: |
June 20, 2017 |
PCT NO: |
PCT/EP2017/065067 |
371 Date: |
February 27, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04C 2/18 20130101; F04C
15/0088 20130101 |
International
Class: |
F04C 2/18 20060101
F04C002/18 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 29, 2016 |
DE |
10 2016 216 159.8 |
Claims
1. An external gear pump (1) having a pump housing (2), wherein an
inlet (2a), an outlet (2b), and a working chamber (6) are formed in
the pump housing (2), wherein a first gear (11), which is arranged
on a first shaft (21), and a second gear (12), which is arranged on
a second shaft (22), are arranged in the working chamber (6) in
such a way that said first and second gears mesh with each other,
wherein both of the first and second gears (11, 12) have teeth
having a tooth width (b), wherein the first shaft (21) is radially
supported in at least one plain bearing (61), and wherein the
second shaft (22) is radially supported in at least one further
plain bearing (63), wherein the one plain bearing (61) has a first
bearing diameter (D.sub.61), and wherein the further plain bearing
(63) has a further bearing diameter (D.sub.63), wherein, during
operation of the external gear pump (1), a delivery volume (V) of a
working medium can be conveyed from the inlet (2a) to the outlet
(2b), characterized in that the ratio V/(D.sub.61.sup.2*b) is
<1.1 and the ratio V/(D.sub.63.sup.2*b) is <1.1.
2. The external gear pump (1) as claimed in claim 1, characterized
in that the ratio V/(D.sub.61.sup.2*b) is >0.5 and the ratio
V/(D.sub.63.sup.2*b) is >0.5.
3. The external gear pump (1) as claimed in claim 1, characterized
in that the first bearing diameter D.sub.61 and the further bearing
diameter D.sub.63 are equal.
4. The external gear pump (1) as claimed in claim 1, characterized
in that the first and second shafts (21, 22) are each radially
supported in two plain bearings (61, 62, 63, 64), wherein, for each
bearing diameter (D.sub.61, D.sub.62, D.sub.63, D.sub.64):
V/(D.sup.2*b)<1.1, where D={D.sub.61; D.sub.62; D.sub.63;
D.sub.64}.
5. The external gear pump (1) as claimed in claim 4, characterized
in that furthermore: D.sub.61=D.sub.62=D.sub.63=D.sub.64.
6. An external gear pump (1) having a pump housing (2), wherein an
inlet (2a), an outlet (2b), and a working chamber (6) are formed in
the pump housing (2), wherein a first gear (11), which is arranged
on a first shaft (21), and a second gear (12), which is arranged on
a second shaft (22), are arranged in the working chamber (6) in
such a way that said first and second gears mesh with each other,
wherein the first gear (11) has a first tip diameter (DK.sub.11)
and the second gear (12) has a second tip diameter (DK.sub.12),
wherein the first shaft (21) is radially supported in at least one
plain bearing (61) and wherein the second shaft (22) is radially
supported in at least one further plain bearing (63), wherein the
first and second shafts (21, 22) are arranged parallel with a
center distance (a) with respect to each other, wherein the one
plain bearing (61) has a first bearing diameter (D.sub.61) and
wherein the further plain bearing (63) has a further bearing
diameter (D.sub.63), characterized in that the ratio
(DK.sub.11*a)/D.sub.61.sup.2 is <2.5 and the ratio
(DK.sub.12*a)/D.sub.63.sup.2 is <2.5.
7. The external gear pump (1) as claimed in claim 6, characterized
in that the ratio (DK.sub.11*a)/D.sub.61.sup.2 is >1.5 and in
that the ratio (DK.sub.12*a)/D.sub.63.sup.2 is >1.5.
8. The external gear pump (1) as claimed in claim 6, characterized
in that the first bearing diameter D.sub.61 and the further bearing
diameter D.sub.63 are equal.
9. The external gear pump (1) as claimed in claim 6, characterized
in that the first and second shafts (21, 22) are each radially
supported in two plain bearings (61, 62, 63, 64), wherein, for each
bearing diameter (D.sub.61, D.sub.62, D.sub.63, D.sub.64):
(DK*a)/D.sup.2 is <2.5 where DK={DK.sub.11; DK.sub.12} and where
D={D.sub.61; D.sub.62; D.sub.63; D.sub.64}.
10. The external gear pump (1) as claimed in claim 9, characterized
in that furthermore: D.sub.61=D.sub.62=D.sub.63=D.sub.64.
11. A heat recovery system having a circuit that carries a working
medium, wherein the circuit comprises a feed fluid pump, an
evaporator, an expansion machine (104) and a condenser in the flow
direction of the working medium, characterized in that the feed
fluid pump is embodied as an external gear pump (1) as claimed in
claim 1.
12. The external gear pump (1) as claimed in claim 1, characterized
in that the ratio V/(D.sub.61.sup.2*b) is >1.0 and the ratio
V/(D.sub.63.sup.2*b) is >1.0.
13. The external gear pump (1) as claimed in claim 6, characterized
in that the ratio (DK.sub.11*a)/D.sub.61.sup.2 is >2.0 and the
ratio (DK.sub.12*a)/D.sub.63.sup.2 is >2.0.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an external gear pump, in
particular one embodied as a feed fluid pump of a waste heat
recovery system of an internal combustion engine.
[0002] There are many instances of fluid delivery pumps in the
prior art, e.g. in the form of external gear pumps from German
Laid-Open Application DE 10 2009 045 030 A1.
[0003] Moreover, the arrangement of feed fluid pumps within a waste
heat recovery system of an internal combustion engine is also known
in principle, e.g. from German Laid-Open Application DE 10 2013 205
648 A1. However, the known documents leave open the question of how
the feed fluid pump can be operated with the longest possible
service life, even with aggressive working media in heat recovery
systems, which have a very low viscosity.
SUMMARY OF THE INVENTION
[0004] In contrast, the external gear pump according to the
invention has the advantage that it can be used for low-viscosity
working media that are poor lubricants and can form a hydrodynamic
lubricating film in the plain bearings, even for such working
media. The bearing service life is thereby significantly
increased.
[0005] For this purpose, the external gear pump has a pump housing.
An inlet, an outlet, and a working chamber are formed in the pump
housing. A first gear, which is arranged on a first shaft, and a
second gear, which is arranged on a second shaft, are arranged in
the working chamber in such a way that said first and second gears
mesh with each other. Both gears have teeth having a tooth width b.
The first shaft is radially supported in at least one plain
bearing, and the second shaft is radially supported in at least one
further plain bearing. The plain bearing has a bearing diameter
D.sub.61, and the further plain bearing has a further bearing
diameter D.sub.63. During operation of the external gear pump 1, a
delivery volume V of a working medium can be conveyed from the
inlet to the outlet. The two bearing diameters D.sub.61, D.sub.63
are designed in such a way that the ratio V/(D.sub.61.sup.2*b) is
<1.1 and that the ratio V/(D.sub.63.sup.2*b) is <1.1.
[0006] It is furthermore advantageous if the ratio
V/(D.sub.61.sup.2*b) is >0.5, in particular greater than 1.0.
Similarly also, the ratio V/(D.sub.63.sup.2*b) is >0.5, in
particular greater than 1.0. These two ratios should therefore not
be arbitrarily small since the delivery volume V approaching zero
and dimensions approaching infinity make no sense for the external
gear pump according to the invention.
[0007] The design of the external gear pump runs contrary to the
typical manner of proceeding of a person skilled in the art, who
would wish to achieve a delivery volume V which is as high as
possible combined with dimensions of the components of the external
gear pump which are as small as possible.
[0008] The plain bearings can be designed as bearing bores in the
pump housing, or in a double bearing seat or bearing bush arranged
therein, for example. The delivery volume V is the volume of the
working medium delivered to the outlet at typical operating
points.
[0009] Owing to the atypical large bearing diameters that are used
as a result for the plain bearings of the external gear pump,
low-viscosity working media that are poor lubricants can be
delivered without having to hermetically seal the plain bearings
relative to the working chamber. Even working media with a
kinematic viscosity<<2 mm.sup.2/s can be delivered in this
way. The contact surfaces between the shafts and the plain bearings
are increased by this design, and therefore a hydrodynamic sliding
film can form in the plain bearings during operation. The wear in
the plain bearings is thereby significantly reduced and,
accordingly, the service life of the plain bearings and hence also
of the entire external gear pump is increased. In the best case, it
is even possible to dispense with expensive, particularly
wear-resistant materials for the plain bearings.
[0010] In preferred developments, the two bearing diameters of the
plain bearing and of the further plain bearing are equal. As a
result, the two plain bearings can be of unitary design. It is
furthermore also possible to choose gears of the same size, thus
optimizing the efficiency of the external gear pump.
[0011] In advantageous embodiments, the two shafts are each
radially supported in two plain bearings, advantageously on both
sides of the gears. The above design formula then applies to all
four plain bearings, i.e. V/(D.sup.2*b)<1.1, where D={D.sub.61;
D.sub.62; D.sub.63; D.sub.64}, wherein D.sub.61, D.sub.62,
D.sub.63, D.sub.64 are the four bearing diameters. All four bearing
diameters are then also preferably equal:
D.sub.61=D.sub.62=D.sub.63=D.sub.64.
[0012] Alternative design concepts and also design concepts that
can be combined with the above designs are described below. Here,
the following design concepts are independent of the delivery
volume V.
[0013] For this purpose, the external gear pump has a pump housing.
An inlet, an outlet, and a working chamber are formed in the pump
housing. A first gear, which is arranged on a first shaft, and a
second gear, which is arranged on a second shaft, are arranged in
the working chamber in such a way that said first and second gears
mesh with each other. The first gear has a first tip diameter
DK.sub.11 and the second gear has a second tip diameter DK.sub.12,
wherein preferably both tip diameters DK.sub.11, DK.sub.12 are
equal. The first shaft is radially supported in at least one plain
bearing and the second shaft is radially supported in at least one
further plain bearing. The two shafts are arranged parallel with a
center distance a with respect to each other. The plain bearing has
a bearing diameter D.sub.61 and the further plain bearing has a
further bearing diameter D.sub.63. The two bearing diameters
D.sub.61, D.sub.63 are designed in such a way that the ratio
(DK.sub.11*a)/D.sub.61.sup.2 is <2.5 and that the ratio
(DK.sub.12*a)/D.sub.63.sup.2 is <2.5.
[0014] The ratio is furthermore advantageously
(DK.sub.11*a)/D.sub.61.sup.2>1.5--in particular greater than
2.0. Similarly also, the ratio (DK.sub.12*a)/D.sub.63.sup.2 is
>1.5--in particular greater than 2.0. These two ratios should
therefore not become arbitrarily small since the tip diameters and
the center distance approaching zero and bearing diameters
approaching infinity make no sense for the external gear pump
according to the invention.
[0015] The design of the external gear pump runs contrary to the
typical manner of proceeding of a person skilled in the art, who
would always wish to make the bearing diameters as small as
possible.
[0016] In these embodiments too, the plain bearings can be designed
as bearing bores in the pump housing, or in a double bearing seat
or bearing bush arranged therein, for example.
[0017] Owing to the atypical large bearing diameters that are used
by this design concept for the plain bearings of the external gear
pump, low-viscosity working media that are poor lubricants can be
delivered without having to hermetically seal the plain bearings
relative to the working chamber. The same advantages as those
already described above apply.
[0018] There are likewise also the same developments of the
invention as above: the radial support for the two shafts by two
plain bearings in each case and the use of equal bearing diameters
for all the plain bearings, wherein each bearing diameter should be
dimensioned in accordance with the design concept.
[0019] External gear pumps are very well-suited to use in waste
heat recovery systems of internal combustion engines. Waste heat
recovery systems of this kind often use low-viscosity working media
that are poor lubricants. The external gear pump according to the
invention can therefore be used very advantageously in a waste heat
recovery system. The waste heat recovery system has a circuit that
carries a working medium, wherein the circuit comprises a feed
fluid pump, an evaporator, an expansion machine and a condenser in
the flow direction of the working medium. Here, the feed fluid pump
is embodied as an external gear pump having the features described
above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Illustrative embodiments of the invention are described in
greater detail below with reference to the attached drawings, in
which:
[0021] FIG. 1 shows an external gear pump from the prior art in an
exploded illustration, wherein only the essential regions are
illustrated,
[0022] FIG. 2 shows a schematic sectional illustration through an
external gear pump from the prior art,
[0023] FIG. 3 shows an external gear pump in longitudinal section,
wherein only the essential regions are illustrated.
DETAILED DESCRIPTION
[0024] An external gear pump 1 from the prior art is shown in an
exploded illustration in FIG. 1. The external gear pump 1 comprises
a pump housing 2, a cover 3 and a bottom flange 4. The cover 3 and
the bottom flange 4 are clamped to one another by four screws 5
with the pump housing 2 in between. The pump housing 2, the cover 3
and the bottom flange 4 delimit a working chamber 6.
[0025] A first gear 11 and a second gear 12 are arranged in the
working chamber 6 in such a way that said first and second gears
mesh with each other. In this case, both gears 11, 12 have a
certain number of teeth, each having a tooth width or gear width b.
The first gear 11 is secured on a first shaft 21, and the second
gear 12 is secured on a second shaft 22 parallel to the first shaft
21. Here, the first shaft 21 serves as a drive shaft and is
connected to a drive (not illustrated), e.g. a crankshaft of an
internal combustion engine. For this purpose, the first shaft 21
projects through the bottom flange 4.
[0026] The two shafts 21, 22 each project through the gear 11, 12
associated therewith and are connected firmly thereto, in each case
by a press fit, for example. The shafts 21, 22 are supported on
both sides of the gears 11, 12. Support is provided by two double
bearing seats 30, 40, wherein the double bearing seats 30, 40 are
arranged in the working chamber 6: one double bearing seat 30 is
arranged adjacent to the bottom flange 4, and a further double
bearing seat 40 is arranged adjacent to the cover 3. Two bearing
bushes 9 are press-fitted in each of the two double bearing seats
30, 40. The bearing bushes 9 of the double bearing seat 30 support
the two shafts 21, 22 on the drive side, and the bearing bushes 9
of the further double bearing seat 40 support them on the opposite
side of the gears 11, 12. The bearing bushes 9 thus form plain
bearings for the two shafts 21, 22. As an alternative, the two
bearing bushes 9 can also be embodied integrally with the double
bearing seat 30. The same also applies to the further double
bearing seat 40.
[0027] The four bearing bushes 9 each have a radial bearing
function and each form a plain bearing with the shaft 21, 22
associated therewith. The axial bearing function is achieved by
means of the two double bearing seats 30, 40: for this purpose,
double bearing seat 30 has a stop surface 31 on an end face, and
the further double bearing seat 40 has a further stop surface 42 on
an end face. Both stop surfaces 31, 42 interact with both gears 11,
12. Stop surface 31 supports both gears 11, 12 in the axial
direction oriented toward the bottom flange 4; the further stop
surface 42 supports both gears 11, 12 in the axial direction
oriented toward the cover 3.
[0028] To seal off the working chamber 6 with respect to the
surroundings, two seals are arranged on the pump housing 2: a seal
28 between the pump housing 2 and the bottom flange 4 and a further
seal 29 between the pump housing 2 and the cover 3. Both seals 28,
29 extend approximately in a ring shape over the circumference of
the pump housing 28, 29 and are usually arranged in corresponding
grooves.
[0029] An axial field seal 18 is furthermore arranged between
double bearing seat 30 and the bottom flange 4, and a further axial
field seal 19 is arranged between the further double bearing seat
40 and the cover 3. On the one hand, the two axial field seals 18,
19 provide axial support for the two double bearing seats 30, 40
within the pump housing 2. On the other hand, the end faces or rear
sides of the two double bearing seats 30, 40 are thereby subjected
either to the pressure level of the pressure zone or to the
pressure level of the suction zone, depending on the angle of
rotation.
[0030] FIG. 2 shows the principle of action of the external gear
pump 1 known from the prior art in a schematic sectional
illustration. An inlet 2a and an outlet 2b, which open into the
working chamber 6 on opposite sides, are formed in the pump housing
2. A delivery volume V of the working medium is thus conveyed from
the inlet 2a to the outlet 2b on the housing wall of the pump
housing 2 between the teeth of the two gears 11, 12. Here, the
delivery volume V corresponds to the volume delivered in rated
operation of the external gear pump 1, i.e. to the volume delivered
at significant operating points. In respect of the tooth width b of
the two gears 11, 12, a specific delivery volume V.sub.spec=V/b is
thus obtained.
[0031] As a result, the suction zone of the external gear pump 1
with a low first pressure level--e.g. atmospheric pressure--is
formed in the region of the inlet 2a, and the pressure zone of the
external gear pump 1 with a higher, second pressure level--e.g. 40
bar--is formed in the region of the outlet 2b. Here, the second
pressure level of the pressure zone depends on the following flow
topology, e.g. on a restriction.
[0032] The tip diameter DK.sub.11 of the first gear 11 and the tip
diameter DK.sub.12 of the second gear 12 are furthermore
illustrated, as is the center distance a between the two shafts 21,
22. Preferably, the two tip diameters DK.sub.11, DK.sub.12 are
equal and the two gears 11, 12 have the same number of teeth.
[0033] FIG. 3 shows a cross section of an external gear pump 1
according to the invention in the region through the longitudinal
axes of the two shafts 21, 22, which are arranged parallel to one
another at a center distance a. According to the invention, the
diameters of the plain bearings 61, 62, 63, 64 of the two shafts
21, 22 are made significantly larger than in the case of
conventional external gear pumps. As a result, the external gear
pump 1 according to the invention is suitable for low-viscosity
(e.g. for viscosities<<2 mm.sup.2/s) and working media that
are poor lubricants. The external gear pump 1 according to the
invention is therefore particularly well-suited for use in waste
heat recovery systems of internal combustion engines.
[0034] The gear pair, i.e. the two gears 11, 12, are supported by
means of plain bearings 61, 62, 63, 64. In the embodiment in FIG.
3, support is provided in two two-part double bearing seats 30, 40.
However, the two double bearing seats 30, 40 can also be of
integral construction. As an option, it is also possible to use
bearing bushes, as depicted in FIG. 1. In this case, double bearing
seat 30 and the further double bearing seat 40 can also be of
different construction, as before.
[0035] Double bearing seat 30 is supported via the axial field seal
18 on the bottom flange 4, and the further double bearing seat 40
is supported via the further axial field seal 19 on the cover 3.
Both double bearing seats 30, 40 are thus supported in the pump
housing 2 via the two axial field seals 18, 19 and the shafts 21,
22 arranged therebetween and via gears 11, 12.
[0036] A through-drive shaft opening 15 is formed in the bottom
flange 4. As a result, the drive shaft of the external gear pump 1,
in this case the first shaft 21, can be passed out of the pump
housing 2 and coupled to a drive, e.g. a coupling or a belt.
[0037] Four bearing bores 51, 52, 53, 54 are formed in the double
bearing seats 30, 40, with the result that the first shaft 21 is
supported by means of the first bearing bore 51 and by means of the
second bearing bore 52, and with the result that the second shaft
22 is supported by means of the third bearing bore 53 and by means
of the fourth bearing bore 54. Three bearing bores 52, 53, 54 are
embodied as blind bores, while the first bearing bore 51 is
embodied as a through bore, thus enabling the first shaft 21, which
is embodied as a drive shaft, to be passed out of double bearing
seat 30.
[0038] The four bearing bores 51, 52, 53, 54 each form a plain
bearing 61, 62, 63, 64 for the shafts 21, 22. The first shaft 21 is
supported in two plain bearings 61, 62, wherein the two plain
bearings 61, 62 are arranged on opposite sides of the first gear 11
when viewed in the axial direction. The second shaft 22 is
supported in two further plain bearings 63, 64, wherein the two
further plain bearings 63, 64 are arranged on opposite sides of the
second gear 12 when viewed in the axial direction.
[0039] In alternative embodiments, the external gear pump 1 has
just one plain bearing for each shaft 21, 22. That is to say, for
example, the first shaft 21 is then radially supported only by
plain bearing 61, and the second shaft 22 is radially supported
only by the further plain bearing 63 within the pump housing 2.
[0040] According to the invention, the plain bearings 61, 62, 63,
64, unlike the conventional designs, are provided with particularly
large bearing diameters D.sub.61, D.sub.62, D.sub.63, D.sub.64. The
individual bearing diameters D.sub.61, D.sub.62, D.sub.63, D.sub.64
are configured in such a way that: [0041] in respect of the
specific delivery volume V.sub.spec: V.sub.spec/D.sup.2<1.1
[0042] in respect of the delivery volume V: V/(D.sup.2b)<1.1
wherein D={D.sub.61; D.sub.62; D.sub.63; D.sub.64}.
[0043] Here, it is advantageous if
D.sub.61=D.sub.62=D.sub.63=D.sub.64.
[0044] As an alternative or in addition, the bearing diameters
D.sub.61, D.sub.62, D.sub.63, D.sub.64 of the plain bearings 61,
62, 63, 64 should be configured in relation to the tip diameter
DK.sub.11, DK.sub.12 of the two gears 11, 12 and in relation to the
center distance a of the two shafts 21, 22 relative to one another.
Here, the following should apply: (DK*a)/D.sup.2<2.5, where
DK={DK.sub.11; DK.sub.12} and D={D.sub.61; D.sub.62; D.sub.63;
D.sub.64}.
[0045] The peripheral speed of the cylindrical contact surfaces of
the shafts 21, 22 in the plain bearings 61, 62, 63, 64 is thereby
increased to such an extent that the radial sliding support with a
given low-viscosity working medium and a given, relatively low
delivery volume V of the external gear pump 1 functions in the
hydrodynamic mode, that is to say a lubricating film can build up
between the shafts 21, 22 and the plain bearings 61, 62, 63, 64.
For this purpose, the aim is to make the bearing diameter D.sub.61,
D.sub.62, D.sub.63, D.sub.64 of the plain bearings 61, 62, 63, 64
as large as possible, and therefore a tooth system of the two gears
11, 12 is chosen which, on the one hand, still rolls cleanly in
mechanical terms and allows adequate hydraulic seals with respect
to the pump housing 2, the cover 3 and the bottom flange 4 without
producing an excessive delivery volume V, wherein the delivery
volume V should be suitable, in particular, for a waste heat
recovery system.
[0046] The object of designing the external gear pump 1 in such a
way that the sliding speed between the shaft 21, 22 and the plain
bearings 61, 62, 63, 64 is very greatly increased does not arise in
the project planning for a conventional external gear pump
corresponding to the prior art for the usual higher-viscosity
working media. In that case, it is namely possible, for a given
delivery volume, to optimize as regards a compact installation
space, i.e. in the direction of plain bearings which are as small
as possible. A hydrodynamic lubricating film would nevertheless be
established in the contact locations of the plain bearings.
[0047] The invention is defined in such a way that a ratio of the
specific delivery volume V.sub.spec of the delivery tooth system
[mm.sup.3 delivery volume V per millimeter of gear width b] in
relation to the square of the bearing diameter D of the plain
bearings is less than 1.1. Pumps according to the prior art
generally have a ratio of 2 and above in this respect.
Alternatively, another ratio of the product of the tip diameter DK
and the center distance a divided by the square of the bearing
diameter D is less than 2.5. Pumps according to the prior art
generally have a further ratio of this kind of 3 and above.
[0048] In particularly advantageous embodiments, the external gear
pump 1 according to the invention is arranged in a waste heat
recovery system of an internal combustion engine. The internal
combustion engine is supplied with oxygen via an air inlet; the
exhaust gas expelled after the combustion process is discharged
from the internal combustion engine through an exhaust line.
[0049] The waste heat recovery system has a circuit that carries a
working medium, which comprises a feed fluid pump, an evaporator,
an expansion machine and a condenser in the flow direction of the
working medium. The working medium can be fed into the circuit from
a collecting tank and a valve unit via a branch line as required.
As an alternative here, the collecting tank can also be
incorporated into the circuit.
[0050] The evaporator is connected to the exhaust line of the
internal combustion engine and therefore uses the heat energy of
the exhaust gas of the internal combustion engine.
[0051] Liquid working medium is fed into the evaporator by the feed
fluid pump, optionally from the collecting tank, and is evaporated
there by the heat energy of the exhaust gas of the internal
combustion engine. The evaporated working medium is then expanded
in the expansion machine, releasing mechanical energy, e.g. to a
generator (not illustrated) or a transmission (not illustrated).
The working medium is then condensed again in the condenser and
returned to the collecting tank or fed to the feed fluid pump.
[0052] Here, the feed fluid pump of the waste heat recovery system
is an external gear pump 1 according to one of the above
embodiments.
* * * * *