U.S. patent application number 13/656879 was filed with the patent office on 2013-04-25 for delivery pump for a fluid, metering device having the delivery pump and motor vehicle having the metering device.
This patent application is currently assigned to EMITEC GESELLSCHAFT FUER EMISSIONSTECHNOLOGIE MBH. The applicant listed for this patent is EMITEC GESELLSCHAFT FUER EMISSIONSTE. Invention is credited to GEORGES MAGUIN.
Application Number | 20130098005 13/656879 |
Document ID | / |
Family ID | 47022573 |
Filed Date | 2013-04-25 |
United States Patent
Application |
20130098005 |
Kind Code |
A1 |
MAGUIN; GEORGES |
April 25, 2013 |
DELIVERY PUMP FOR A FLUID, METERING DEVICE HAVING THE DELIVERY PUMP
AND MOTOR VEHICLE HAVING THE METERING DEVICE
Abstract
A delivery pump for delivering a fluid includes a delivery
piston to be moved in a delivery direction from a pump inlet to a
pump outlet. The delivery piston is supported in an axial bearing
having a cooling device for cooling the axial bearing with the
fluid. A metering device having the delivery pump and a motor
vehicle having the metering device are also provided.
Inventors: |
MAGUIN; GEORGES; (MARLY,
FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EMITEC GESELLSCHAFT FUER EMISSIONSTE; |
LOHMAR |
|
DE |
|
|
Assignee: |
EMITEC GESELLSCHAFT FUER
EMISSIONSTECHNOLOGIE MBH
LOHMAR
DE
|
Family ID: |
47022573 |
Appl. No.: |
13/656879 |
Filed: |
October 22, 2012 |
Current U.S.
Class: |
60/295 ;
417/313 |
Current CPC
Class: |
F04B 17/048 20130101;
F04B 35/045 20130101; F04B 53/08 20130101 |
Class at
Publication: |
60/295 ;
417/313 |
International
Class: |
F04B 53/08 20060101
F04B053/08; F04B 53/18 20060101 F04B053/18; F01N 3/08 20060101
F01N003/08 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 21, 2011 |
EP |
11290490.9 |
Claims
1. A delivery pump for delivering a fluid, the delivery pump
comprising: a pump inlet and a pump outlet defining a delivery
direction therebetween; a delivery piston configured to move in
said delivery direction from said pump inlet to said pump outlet;
an axial bearing supporting said delivery piston therein; and a
cooling device associated with said axial bearing and configured to
cool said axial bearing with the fluid.
2. The delivery pump according to claim 1, wherein said cooling
device is also a lubricating device configured to lubricate said
axial bearing with the fluid.
3. The delivery pump according to claim 1, wherein: said axial
bearing is a guide channel configured to support said delivery
piston therein in a sliding manner; and said cooling device is
constructed as at least one passage intersecting said guide channel
and directing the fluid to enter said guide channel through said at
least one passage at least at one entry point of said at least one
passage.
4. The delivery pump according to claim 3, wherein said delivery
piston has at least one recess in vicinity of said at least one
passage, said at least one recess crossing said entry point of said
at least one passage during a delivery movement of said delivery
piston in said axial bearing while delivering the fluid into said
axial bearing.
5. The delivery pump according to claim 1, wherein: said guide
channel of said axial bearing has a guiding surface; said delivery
piston has a piston surface; and said axial bearing is formed with
a gap between said guiding surface and said piston surface, said
gap having a gap width of at least 5 pm [micrometers].
6. The delivery pump according to claim 1, wherein said axial
bearing is configured to produce a backflow of fluid through said
axial bearing counter to said delivery direction.
7. The delivery pump according to claim 1, which further comprises:
a delivery chamber having at least one chamber inlet opening
opening into said delivery chamber; and at least one nonreturn
valve disposed between said delivery chamber and said pump outlet
in said delivery direction; said delivery piston configured to
perform a delivery movement into said delivery chamber while
pushing fluid present in said delivery chamber out through said
nonreturn valve in said delivery direction to said pump outlet.
8. A metering device for delivering a reducing agent from a tank
into an exhaust gas treatment device, the metering device
comprising: a delivery line leading from the tank to the exhaust
gas treatment device; and a delivery pump according to claim 1
disposed in said delivery line and configured to deliver reducing
agent as the fluid from the tank to the exhaust gas treatment
device.
9. A motor vehicle, comprising: an internal combustion engine; a
tank for reducing agent; an exhaust gas treatment device for
cleaning exhaust gases from said internal combustion engine; and a
metering device including a delivery line leading from said tank to
said exhaust gas treatment device and a delivery pump according to
claim 1 disposed in said delivery line and configured to meter the
reducing agent from said tank to said exhaust gas treatment device.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the priority, under 35 U.S.C.
.sctn.119, of European Patent Application EP 11 290 490.9, filed
Oct. 21, 2011; the prior application is herewith incorporated by
reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a delivery pump for a fluid, which
can be used in a metering device, for example, to meter a fluid
from a tank into an exhaust gas treatment device for cleaning
exhaust gases from an internal combustion engine. The invention
also relates to a metering device having the delivery pump and a
motor vehicle having the metering device.
[0004] Exhaust gas treatment devices in which a fluid is fed in for
the purpose of cleaning the exhaust gases are widely used,
especially in the motor vehicle sector.
[0005] One exhaust gas cleaning method, which is carried out
particularly often in such exhaust gas treatment devices, is that
of the selective catalytic reduction or SCR method, in which
nitrogen oxide compounds in the exhaust gas are reduced through the
use of a reducing agent. Ammonia is generally used as the reducing
agent in that case. In motor vehicles, ammonia is normally not
stored in the pure form but in the form of a precursor solution or
precursor fluid, which can be converted into ammonia.
[0006] An aqueous urea solution is used, for example, as the
precursor solution. A 32.5% aqueous urea solution, which can be
obtained under the trademark AdBlue.RTM., is used particularly
often.
[0007] That precursor solution can then be fed in to the exhaust
gas in liquid form and then converted into ammonia in the exhaust
gas by purely thermal measures or by hydrolytic measures with
support from a hydrolysis catalytic converter. It is also possible
for the precursor solution to be converted to ammonia outside the
exhaust gas in a reactor provided for that purpose.
[0008] A delivery pump is normally required in order to deliver the
solution from a tank to the exhaust gas treatment device or to a
reactor. The delivery pump must make the reducing agent available
to the exhaust gas treatment device during the entire period of
operation of a motor vehicle. The delivery pump must therefore have
a very long service life. Moreover, the delivery pump should be as
inexpensive as possible.
[0009] A delivery pump for reducing agent is known, for example,
from German Patent DE 10 2008 010 073 B4.
SUMMARY OF THE INVENTION
[0010] It is accordingly an object of the invention to provide a
delivery pump for a fluid, a metering device having the delivery
pump and a motor vehicle having the metering device, which overcome
the hereinafore-mentioned disadvantages and further mitigate the
technical problems of the heretofore-known pumps, devices and
vehicles of this general type. In particular, the intention is to
describe a further improved, particularly advantageous delivery
pump for a fluid which is suitable especially for delivering
reducing agent.
[0011] With the foregoing and other objects in view there is
provided, in accordance with the invention, a delivery pump for
delivering a fluid. The delivery pump comprises a pump inlet and a
pump outlet defining a delivery direction therebetween. A delivery
piston is configured to move in the delivery direction from the
pump inlet to the pump outlet. An axial bearing supports the
delivery piston therein. A cooling device is associated with the
axial bearing and configured to cool the axial bearing with the
fluid.
[0012] The delivery pump is suitable especially for delivering
reducing agent and, in particular, aqueous ammonia solution as a
fluid.
[0013] The delivery pump is preferably suitable for making the
fluid available at a defined pressure at the pump outlet or for
achieving a defined increase in the pressure of the fluid from the
pump inlet to the pump outlet. For this purpose, a delivery pump
drive can be controlled by a control unit, in which the control
unit receives information from at least one pressure sensor for the
purpose of adjusting the defined pressure or the defined increase
in pressure. The control unit can control the delivery pump drive
on the basis of information from at least one pressure sensor. The
delivery pump drive is preferably a drive coil. When an electric
current flows through the drive coil, the drive coil produces an
electromagnetic force which acts on the delivery piston of the
delivery pump. The delivery piston can be set in motion by the
force of the drive coil. The drive can also have a spring which can
exert a restoring force on the delivery piston. By way of example,
a drive coil can be set up to move the delivery piston towards the
pump outlet in the delivery direction, counter to a spring, when a
current flows through the drive coil. The spring can be set up to
return the delivery piston towards the pump inlet, counter to the
delivery direction, when no current is flowing through the drive
coil and the drive coil is therefore not exerting any force on the
delivery piston.
[0014] The pump inlet is preferably constructed for the connection
of an intake line, through which the delivery pump can draw in
fluid from a tank, for example. The pump outlet is preferably
constructed for the connection of a pressure line, into which the
delivery pump can deliver fluid, e.g. towards an exhaust gas
treatment device or towards an injector which opens into an exhaust
gas treatment device. In order to connect the intake line and the
pressure line, the pump inlet and the pump outlet preferably have
corresponding connectors, to which the lines can be detachably
connected. The delivery piston is preferably disposed on a common
axis together with the pump inlet and the pump outlet.
[0015] The axial bearing preferably allows movement of the delivery
piston only in an axial direction extending along the delivery
direction from the pump inlet to the pump outlet. Rotation or
translational displacement of the delivery piston is preferably
prevented by the axial bearing. The axial bearing is preferably a
plain or slide bearing. The delivery piston has a piston surface,
and the axial bearing has a guiding surface. The piston surface and
the guiding surface can slide upon one another.
[0016] Details of the construction of such a delivery pump may be
obtained in this case by making reference especially to German
Patent DE 10 2008 010 073 B4, which illustrates the construction
thereof in detail in FIG. 2 and provides explanations pertaining
thereto in paragraphs [0039] to [0045]. FIG. 2 and the paragraphs
thereof mentioned above are hereby incorporated herein in full by
reference.
[0017] As the piston surface and the guiding surface slide upon one
another in the axial bearing, heat is generated by friction. The
cooling device is preferably set up to deliver the fluid into the
axial bearing and preferably to the piston surface and the guiding
surface in order to absorb and, where appropriate, carry away heat
from the axial bearing. It has been found that high temperatures in
the axial bearing of a delivery pump can drastically shorten the
life of the delivery pump. This is the case especially when the
delivery pump is used to deliver aqueous urea solution. At high
temperatures, urea precipitates may form in the aqueous urea
solution. Those precipitates act like abrasive particles in the
delivery pump and especially in a plain bearing and can damage the
bearing and the delivery pump. It is therefore advantageous,
especially for delivery pumps for delivering aqueous urea solution,
to carry away the heat produced in a plain bearing. It is
particularly advantageous for this purpose to use the fluid which
is already available in the delivery pump.
[0018] In accordance with another particularly advantageous feature
of the invention, the cooling device is simultaneously a
lubricating device for lubricating the axial bearing with the
fluid.
[0019] An axial bearing which is embodied as a plain bearing is
generally advantageous if a lubricant is provided. The lubricant
reduces the friction between the surfaces in the plain bearing. In
the delivery pumps considered herein, the surfaces of the plain
bearing are preferably a piston surface of the delivery piston and
a guiding surface of a guide bore of the axial bearing in which the
piston is guided. It is particularly preferred if a gap, in which a
lubricating film formed of the fluid is formed, is provided between
the piston surface and the guiding surface.
[0020] By virtue of the fact that the fluid is simultaneously used
as a coolant and a lubricant for the axial bearing of the delivery
pump, it may be possible to dispense with an additional lubricant
for the axial bearing.
[0021] In accordance with a further particularly advantageous
feature of the invention, the axial bearing is a guide channel, in
which the delivery piston is supported in a sliding manner, and the
cooling device is embodied as at least one passage, which
intersects the guide channel and through which the fluid enters the
guide channel at least at one entry point.
[0022] The shape of the guide channel is preferably matched to a
cross section of the delivery piston to enable the delivery piston
to be moved backwards and forwards in the guide channel in a
delivery movement. The passage can be a bore, a gap or a slot, for
example, which meets the guide channel and thus intersects the
guide channel.
[0023] A plurality of passages is preferably disposed along the
guide channel to enable the axial bearing or guide channel or
guiding surface and the piston surface to be wetted as fully as
possible with fluid. As another preferred option, a plurality of
passages is also disposed around the delivery piston and the
guiding channel in the circumferential direction to ensure complete
wetting. For example, two to eight passages leading to the guide
channel and distributed uniformly in the circumferential direction
are in each case provided in two to six planes along the guide
channel.
[0024] The passages can be embodied as bores, gaps or the like, for
example. The passages establish a connection through which the
fluid can pass into the axial bearing or guide channel. This
connection preferably extends from a channel through the delivery
pump through which the fluid passes on the way from the pump inlet
to the pump outlet or along which channel the fluid flows during
normal delivery.
[0025] The passages described herein are a technically particularly
uncomplicated and effective configuration for passing the fluid
into the axial bearing.
[0026] In accordance with an added particularly advantageous
feature of the invention, the delivery piston has at least one
recess in the region of the passage. The recess crosses the entry
point of the passage during a delivery movement of the delivery
piston in the axial bearing and, in the process, delivers the fluid
into the axial bearing.
[0027] The delivery piston preferably has a largely flat piston
surface matched to the shape or guiding surface of the guide
channel. Both the piston surface and the guiding surface preferably
have a low roughness of, for example, less than 10 .mu.m
[micrometers] and preferably even less than 5 .mu.m [micrometers].
The roughness of these surfaces is low in order to reduce the
friction of the delivery piston in the guide channel of the axial
bearing. The recess forms a re-entrant area of the delivery piston
relative to the piston surface. The recess can be embodied as a
single notch or opening in the delivery piston. It is also possible
for the recess to form a complete network or complete system of
channels on the piston surface, through which the fluid can pass,
and thus allow distribution of the fluid over the piston surface
and over the guiding surface. When the recess crosses the passage,
an area of the recess and an area of the entry point of the passage
overlap at least partially in an overlap zone. The fluid can then
enter the recess from the passage. The delivery movement changes
the area of the overlap zone because the entry point and the recess
move relative to one another. During the delivery movement, there
is preferably at least at times no overlap at all between the area
of the entry point and the area of the recess. Indeed, the recess
preferably crosses several different passages during the delivery
movement. The fluid pressures prevailing at these different
passages are preferably different. The fluid can thus be delivered
effectively through the axial bearing by the recess.
[0028] The use of at least one recess in the delivery piston for
delivering the fluid into the axial bearing is particularly
advantageous because the fluid is delivered effectively into the
axial bearing and there is no need for any additional moving parts
(such as an additional pump) for delivering the fluid into the
axial bearing.
[0029] In accordance with an additional particularly advantageous
feature of the invention, the axial bearing is embodied with a gap
between a guiding surface of a guide channel of the axial bearing
and a piston surface of the delivery piston, in which the gap has a
gap width of at least 5 .mu.m [micrometers].
[0030] Such a gap width between the piston surface and the guiding
surface is particularly advantageous in ensuring that a film of the
fluid forms in the axial bearing or guide channel or gap, with this
film being particularly advantageous for cooling and, where
appropriate, also for lubricating the axial bearing.
[0031] In accordance with yet another particularly advantageous
feature of the invention, the axial bearing is set up in such a way
that a backflow of fluid through the axial bearing counter to the
delivery direction of the delivery pump is obtained.
[0032] The backflow preferably covers the entire length of the
axial bearing. In this way, particularly effective cooling of the
axial bearing can be achieved. It also ensures that cooling of the
axial bearing is uniformly distributed over the entire length of
the axial bearing and also that no local overheating of the axial
bearing occurs.
[0033] In accordance with yet a further particularly advantageous
feature of the invention, the delivery pump has a delivery chamber,
at least one chamber inlet opening, which opens into the delivery
chamber, and at least one nonreturn valve, which is disposed
between the delivery chamber and the pump outlet in the delivery
direction, wherein the delivery piston can perform a delivery
movement into the delivery chamber and, in the process, pushes
fluid present in the delivery chamber out through the nonreturn
valve in the delivery direction to the pump outlet.
[0034] During the delivery movement, the delivery piston moves into
and out of the delivery chamber in a regular manner. During the
delivery movement of the delivery piston, the volume of the
delivery chamber is thus increased and reduced in a regular manner.
In a particularly advantageous variant of the delivery pump, the
reduction in the volume is such that the minimum volume of the
delivery chamber which occurs during the delivery movement is at
least ten times, preferably twenty times, and particularly
preferably one hundred times, less than the maximum volume of the
delivery chamber which occurs. Fluid can enter the delivery chamber
in the delivery direction through at least one chamber inlet
opening which opens into the delivery chamber. If a plurality of
chamber inlet openings is provided, they are preferably all located
in a common plane aligned perpendicularly to the direction of
movement or to the axis of movement of the delivery piston. This is
possible particularly if the delivery piston is disposed close to a
position of maximum retraction (that is to say in a direction
towards the pump inlet) during the delivery movement and, in this
case, the volume of the delivery chamber is close to the maximum
volume described. During the delivery movement, the delivery piston
preferably passes over the at least one chamber inlet opening. When
the delivery piston is covering the chamber inlet opening, no fluid
can flow into the delivery chamber. When the delivery piston opens
the delivery chamber, fluid can flow into the delivery chamber
through the chamber inlet opening. There is a nonreturn valve
between the delivery chamber and the pump outlet in the delivery
direction. During a part of the delivery movement in the direction
towards the pump outlet, the delivery piston pushes fluid out of
the delivery chamber, through the nonreturn valve, towards the pump
outlet. The nonreturn valve prevents fluid from flowing back into
the delivery chamber from the pump outlet.
[0035] Through the use of a delivery pump constructed in this way,
it is also possible to achieve a delivery pump with a relatively
high metering accuracy. The delivery pump can then be used not only
as a simple delivery pump but also as a metering pump. In the case
of a metering pump, the quantity of fluid delivered by the delivery
pump can be determined precisely. In the case of the delivery pump
described herein, the quantity of fluid delivered is obtained from
the number of delivery strokes of the delivery piston and the
delivery chamber volume which the delivery chamber has when the
delivery piston is just covering the chamber inlet openings. The
delivery quantity can be calculated as the product of this volume
and the number of delivery strokes.
[0036] In order to obtain details of the construction of a delivery
chamber of a delivery pump, reference may be made in this case once
again especially to German Patent DE 10 2008 010 073 B4, which
illustrates and describes the construction of a delivery chamber in
detail in FIG. 2 and in the explanations pertaining thereto in
paragraphs [0039] to [0045]. FIG. 2 and the paragraphs mentioned
are incorporated herein in full by reference.
[0037] With the objects of the invention in view, there is also
provided a metering device for delivering a reducing agent from a
tank into an exhaust gas treatment device. The metering device
comprises a delivery line leading from the tank to the exhaust gas
treatment device, and a delivery pump according to the invention
disposed in the delivery line and configured to deliver reducing
agent as the fluid from the tank to the exhaust gas treatment
device.
[0038] The delivery pump described, as explained above, is
particularly advantageous for delivering reducing agent. It is
therefore particularly advantageous to employ the delivery pump
described in a metering device for reducing agent.
[0039] With the objects of the invention in view, there is
concomitantly provided a motor vehicle, comprising an internal
combustion engine, a tank for reducing agent, an exhaust gas
treatment device for cleaning exhaust gases from the internal
combustion engine, and a metering device including a delivery line
leading from the tank to the exhaust gas treatment device and a
delivery pump according to the invention disposed in the delivery
line and configured to meter the reducing agent from the tank to
the exhaust gas treatment device.
[0040] Other features which are considered as characteristic for
the invention are set forth in the appended claims, noting that the
features presented individually in the claims can be combined in
any technologically meaningful way and can be supplemented by
explanatory material from the description, giving rise to
additional variant embodiments of the invention.
[0041] Although the invention is illustrated and described herein
as embodied in a delivery pump for a fluid, a metering device
having the delivery pump and a motor vehicle having the metering
device, it is nevertheless not intended to be limited to the
details shown, since various modifications and structural changes
may be made therein without departing from the spirit of the
invention and within the scope and range of equivalents of the
claims.
[0042] The construction and method of operation of the invention,
however, together with additional objects and advantages thereof
will be best understood from the following description of specific
embodiments when read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0043] FIG. 1 is a diagrammatic, longitudinal-sectional view of a
variant embodiment of a delivery pump; and
[0044] FIG. 2 is a vertical-sectional view of a motor vehicle
having a metering device with a delivery pump.
DETAILED DESCRIPTION OF THE INVENTION
[0045] Referring now to the figures of the drawings in detail and
first, particularly, to FIG. 1 thereof, there is seen a delivery
pump 1 which can deliver a fluid from a pump inlet 3 to a pump
outlet 4 in a delivery direction 5. In order to deliver the fluid,
the delivery pump 1 has a delivery piston 2, which can be moved
back and forth in an axial bearing 6. During this movement in the
axial bearing 6, the delivery piston 2 performs a delivery movement
11. During the delivery movement 11, the delivery piston 2 moves
into and out of a delivery chamber 18 in a regular manner. During
the delivery movement 11 of the delivery piston 2, the volume of
the delivery chamber 18 is increased and reduced in a regular
manner. In a particularly advantageous variant of the delivery pump
1, the reduction in the volume is such that a minimum volume of the
delivery chamber 18 which occurs during the delivery movement 11 is
at least ten times, preferably twenty times, and particularly
preferably one hundred times, less than the maximum volume of the
delivery chamber 18 which occurs. Fluid can enter the delivery
chamber 18 in the delivery direction 5 through at least one chamber
inlet opening 19 opening into the delivery chamber 18. This is
possible particularly if the delivery piston 2 is disposed close to
a position of maximum retraction (that is to say in a direction
towards the pump inlet 3) during the delivery movement 11 and, in
this case, the volume of the delivery chamber 18 is close to the
maximum volume described. During the delivery movement 11, the
delivery piston 2 preferably passes over the at least one chamber
inlet opening 19. When the delivery piston 2 is covering the
chamber inlet opening 19, no fluid can flow into the delivery
chamber 18. When the delivery piston 2 opens the delivery chamber
18, fluid can flow into the delivery chamber 18 through the chamber
inlet opening 19. There is a nonreturn valve 20 between the
delivery chamber 18 and the pump outlet 4 in the delivery direction
5. During a part of the delivery movement 11 in the direction
towards the pump outlet 4, the delivery piston 2 pushes fluid out
of the delivery chamber 18, through the nonreturn valve 20, towards
the pump outlet 4. The nonreturn valve 20 prevents fluid from
flowing back into the delivery chamber 18 from the pump outlet 4.
The delivery movement 11 of the delivery piston 2 is achieved at
least in part through the use of a drive coil 27. An electric
current can be passed through the drive coil 27. The drive coil 27
then exerts an electromagnetic force on the delivery piston 2, and
the delivery piston 2 is moved. In addition, a non-illustrated
spring can also be provided on the delivery piston 2, exerting a
restoring force on the delivery piston 2 acting counter to a
direction of action of the drive coil 27, for example.
[0046] The axial bearing 6 of the delivery piston 2 is preferably
embodied in the manner of a plain bearing. The axial bearing 6 is
constructed as a guide channel 8, in which the delivery piston 2
lies. The guide channel 8 has a guiding surface 14, and the
delivery piston 2 has a piston surface 15. The guiding surface 14
and the piston surface 15 can slide upon one another, thus allowing
the delivery piston 2 to perform the delivery movement 11 in the
guide channel 8 or axial bearing 6. There is preferably a gap 13
between the piston surface 15 and the guiding surface 14. The gap
has a gap width 16 of at least 5 .mu.m [micrometers], for example,
to enable the piston surface 15 to slide easily on the guiding
surface 14.
[0047] The axial bearing 6 has a cooling device 7. The cooling
device 7 is constructed to deliver the fluid delivered by the
delivery pump 1 into the axial bearing 6 and especially into the
gap 13 between the piston surface 15 and the guiding surface 14. In
the variant embodiment illustrated herein, the cooling device 7 is
at least one passage 9, through which the fluid can enter the axial
bearing 6 or guide channel 8 or gap 13. For this purpose, the
passage 9 intersects the guide channel 8. The passage 9 opens into
the axial bearing or guide channel 8 at an entry point 12. The
passage 9 is constructed as a bore, notch or slot in the wall of
the guide channel 8, for example, and preferably forms a connection
through which the fluid can pass into the axial bearing 6 or guide
channel 8 or gap 13.
[0048] At least one recess 10 is preferably provided in the
delivery piston 2. The recess 10 is disposed in such a way that it
passes over the entry point 12 of the passage 9 when the delivery
piston 2 performs the delivery movement 11. The recess 10 thus
promotes and intensifies the delivery of fluid into the axial
bearing 6 or guide channel 8 or gap 13. A backflow 17 of fluid
through the axial bearing 6 or guide channel 8 or gap 13 counter to
the delivery direction 5 is preferably established.
[0049] FIG. 2 shows a motor vehicle 25 having an internal
combustion engine 26 and an exhaust gas treatment device 23 for
cleaning the exhaust gases of the internal combustion engine 26.
The reducing agent can be delivered from a tank 22 for a reducing
agent into the exhaust gas treatment device 23 through the use of a
metering device 21. The metering device 21 furthermore has a
delivery line 24 from the tank 22 to the exhaust gas treatment
device 23. A delivery pump 1 for delivering the reducing agent is
provided in the delivery line 24.
* * * * *