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.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority, under 35 U.S.C. §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

1. Field of the Invention

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.

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.

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.

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®, is used particularly often.

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.

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.

A delivery pump for reducing agent is known, for example, from German Patent DE 10 2008 010 073 B4.

SUMMARY OF THE INVENTION

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.

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.

The delivery pump is suitable especially for delivering reducing agent and, in particular, aqueous ammonia solution as a fluid.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

The passages described herein are a technically particularly uncomplicated and effective configuration for passing the fluid into the axial bearing.

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.

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 μm [micrometers] and preferably even less than 5 μm [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.

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.

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 μm [micrometers].

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

FIG. 1 is a diagrammatic, longitudinal-sectional view of a variant embodiment of a delivery pump; and

FIG. 2 is a vertical-sectional view of a motor vehicle having a metering device with a delivery pump.

DETAILED DESCRIPTION OF THE INVENTION

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.

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 μm [micrometers], for example, to enable the piston surface 15 to slide easily on the guiding surface 14.

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.

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.

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.

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.