Patent Application
20160138589
1. Field of the Invention
The invention relates to a pump for delivering a liquid, which pump is in particular suitable for delivering a liquid additive into the exhaust line apparatus of an internal combustion engine.
2. Related Art
For the purification of the exhaust gases of internal combustion engines, exhaust-gas treatment devices are known into which a liquid additive is supplied for the purposes of purifying the exhaust gases. An exhaust-gas purification method implemented in such exhaust-gas treatment devices is the selective catalytic reduction (SCR) method in which nitrogen oxide compounds in the exhaust gas are reduced with the aid of a reducing agent. Ammonia in particular is used as reducing agent. Ammonia is often stored in the motor vehicle not directly but in the form of a liquid additive that constitutes a precursor solution of the reducing agent. The liquid additive may be converted to form reducing agent within the exhaust gas in the exhaust-gas treatment device or outside the exhaust gas in a reactor provided specifically for the purpose. For the SCR method, urea-water solution is used as liquid additive. A 32.5% urea-water solution is available under the trade name AdBlue®.
For the delivery of liquid additive out of a tank and for the dosed supply of the liquid additive to the exhaust line apparatus, at least one pump is provided. A pump of this type should be as inexpensive and reliable as possible. It is particularly advantageous if the pump can also perform a dosing function, that is to say delivers a predefined amount of the liquid additive very accurately. Furthermore, during the delivery, the least possible pressure fluctuations should be generated in the liquid additive, because these can adversely affect the spray pattern of a nozzle for atomizing the liquid additive in the exhaust-gas treatment device. A further requirement is that the pump should be as quiet as possible.
A further important aspect in the case of pumps for delivering liquid additives is that the liquid additives for exhaust-gas purification that are used can freeze at low temperatures. The urea-water solution mentioned above, for example, freezes at −11° C. In the automotive field, such low temperatures can arise, for example, during long standstill periods in winter, wherein the liquid additive expands as it freezes. The pump should accordingly also be constructed such that it is not damaged by freezing liquid additive.
Taking this as a starting point, it is an object of the present invention to solve, or at least alleviate, the technical problems highlighted in connection with the prior art. It is sought in particular to describe a particularly advantageous pump for delivering a liquid, which pump is suitable for use in the technical field of exhaust-gas purification.
The objects are achieved, in one aspect, by a pump according to the features disclosed herein. The features specified individually may be combined with one another in any desired technologically meaningful way and may be supplemented by explanatory facts from the description, with further design variants of the invention being highlighted.
According to one aspect, the invention relates to a pump for delivering a liquid, having a pump housing with at least one inlet and at least one outlet, wherein, on the pump housing, there is arranged an eccentric which is rotatable, with an axis, relative to the pump housing. Furthermore, a deformable element is arranged between the pump housing and the eccentric, wherein the deformable element delimits at least one delivery path from the at least one inlet to the at least one outlet and forms at least one displaceable seal of the delivery path, which at least one displaceable seal separates off at least one closed pump volume in the delivery path, and, by way of a movement of the eccentric, the at least one displaceable seal can be displaced in a delivery direction from the inlet to the outlet for the purposes of delivering the liquid along the delivery path. The inlet and the outlet furthermore have an angular spacing to one another in a circumferential direction about the axis, and the seal spans, in the circumferential direction, an angular segment in which the delivery path is closed, wherein the angular segment is larger than the angular spacing.
A pump with the described construction can be referred to as an orbital pump. A gap exists between the pump housing and the eccentric, in which gap the deformable element is arranged. The delivery path is arranged within the gap, and the delivery path is delimited at least by the (single) deformable element, and possibly additionally by the pump housing and/or by the eccentric. The deformable element is preferably arranged in the gap between the eccentric and the pump housing such that, in the region of the at least one seal, the deformable element is pinched or compressed between the housing and the eccentric, such that, in the region of the seal, the gap is completely closed by the deformable element and/or the gap no longer has, there, a cross-sectional area that forms a delivery path through which flow can pass freely. The gap or the delivery path is thereby closed in fluid-tight fashion in the region of the at least one seal. The gap or the delivery path is filled with the liquid during the operation of the pump.
Along the delivery path, the at least one seal divides the delivery path, such that at least one closed pump volume is formed. The expression “closed pump volume” refers, in particular, to a volume within the delivery path, which volume is closed off at least at one side along the delivery path by a seal. It is preferable if, during the operation of the pump, multiple closed pump volumes are displaced from the inlet to the outlet in order to deliver the liquid. Here, a closed pump volume is created (meaning closed off) in the vicinity of the inlet and is then eliminated (opened again) at the outlet. At the inlet, a closed pump volume is closed off by a seal (only) on one side (in a downstream direction), and is connected in an upstream direction to the inlet, such that the liquid can flow through the inlet into the closed pump volume. At the outlet, the closed pump volume is (still) closed off by a seal (only) on one side (this however being in an upstream direction), and is connected in a downstream direction to the outlet, such that the liquid can flow through the outlet out of the closed pump volume. In between, i.e., on the path from the inlet to the outlet, there is a phase in which the closed pump volume is closed off by a seal at both sides.
The pump housing of the pump is preferably a ring or a cylindrical chamber in which the eccentric is arranged centrally at the inside. The pump housing may also be regarded as an external stator of the pump, whereas the eccentric can be referred to as an internal rotor. In a further embodiment of the pump, it is possible for the pump housing to form an internal stator that is surrounded by the eccentric. The eccentric then forms an external rotor. The inlet and the outlet are arranged on the pump housing and permit the inflow and outflow of the liquid into the pump housing and into the delivery path.
It is particularly preferable if the deformable element is a hose laid in an arcuate gap between the eccentric and the pump housing and connecting the inlet to the outlet.
The hose, which is in one piece and/or situated inside and/or fixed in the pump housing, is in this case connected in preferably fluid-tight fashion to the inlet and to the outlet, such that the liquid can enter and exit the delivery path in the hose only through the inlet and through the outlet. The seal is formed by virtue of the hose being compressed there by the eccentric and by the pump housing.
The pump is also advantageous if the deformable element is a deformable diaphragm, and the delivery path from the at least one inlet to the at least one outlet is at least partially delimited by the pump housing and by the deformable diaphragm.
In this design variant, the delivery path is formed between the deformable diaphragm, which is in one piece and/or situated inside and/or fixed in the pump housing, and the pump housing, and constitutes a gap between the pump housing and the deformable diaphragm. To form the seal, the deformable diaphragm is pressed against the pump housing by the eccentric, such that the deformable diaphragm bears against the pump housing and no gap remains between the deformable diaphragm and the pump housing. The deformable diaphragm is preferably, in sections, formed around the pump housing in a U-shape and adhesively bonded to and/or compressed against the pump housing.
In any case, the deformable element is preferably composed of a flexible rubber material, which exhibits high deformability. Deformable elements composed of elastomer materials, for example of natural rubber or of latex, are particularly preferred. To increase the durability and/or to establish and maintain the flexibility, the material of the deformable element may include additives. The deformable element is preferably flexible in all directions, e.g., axially, radially and in the circumferential direction. It is however also possible for the deformable element to exhibit partially directional flexibility. The deformable element may, for example, exhibit greater flexibility in the radial direction than in the circumferential direction and in the axial direction. A deformation of the deformable element in one direction typically also causes a deformation in other spatial directions. The deformable element expands, for example, in the axial direction and/or in the circumferential direction when compressed in the radial direction.
On the pump, there is preferably also provided at least one static seal that prevents an undesired backflow of the liquid from the outlet to the inlet.
The static seal prevents direct bypassing of the delivery path between the outlet and the inlet. Here, a bypass means that the liquid does not cover the entire length of the delivery path but follows a direct, shorter path from the outlet back to the inlet.
If the deformable element is a deformable diaphragm, the latter is preferably ring-shaped and laid into a gap between the eccentric and the housing. The delivery path forms a circular arc segment, and runs in sections in the delivery direction from the inlet to the outlet along the ring-shaped diaphragm. The static seal is arranged along the ring-shaped diaphragm outside the circular arc segment of the delivery path between the inlet and the outlet. By the static seal between the inlet and the outlet, a backflow is reliably prevented.
The static seal may be formed, for example, by a depression or a protrusion of the pump housing, such that a gap between the pump housing and the eccentric is reduced to such an extent that, regardless of the position of the eccentric, the diaphragm is always pinched in the region of the static seal, such that no bypass with respect to the delivery path is formed, and no backflow is possible. The static seal may also be formed by a thickening of the deformable diaphragm in sections in the region of the static seal. By such a thickening of the diaphragm, it can likewise be ensured that a gap between the eccentric and the pump housing is always closed in the region of the static seal.
The static seal may in principle also be realized by virtue of the deformable diaphragm being fastened, for example screwed and/or adhesively bonded, in fluid-tight fashion to the pump housing in the region of the static seal. Such measures likewise effectively prevent a backflow between the deformable diaphragm and the pump housing.
If the deformable element is a hose, no special measures for forming a static seal are necessary, because, in the case of an e.g., fluid-tight hose connected to the inlet and to the outlet, no bypassing can occur. The static seal is then implicitly jointly formed by the wall of the hose.
The eccentric is preferably of multi-part form. The eccentric preferably has an inner region that performs an eccentric rotational movement. Furthermore, an outer bearing ring may be provided that surrounds the inner region. It is preferable for at least one bearing to be situated between the inner region and the outer bearing ring. The bearing may be a ball bearing or a roller bearing. The inner region of the eccentric performs a rotational movement about the axis during operation. The eccentric arrangement, and if appropriate also the external shape of the eccentric, result(s) in an eccentric movement of a surface of the eccentric. The eccentric movement is transmitted to the outer bearing ring. By a bearing between the inner region and a bearing ring, an eccentric rotational movement of the inner region can be converted into an eccentric wobbling movement of the bearing ring without the rotational movement component also being transmitted. The fact that the movement of the bearing ring does not have a rotational movement component makes it possible for shear stresses in the deformable element and internal friction forces of the pump to be reduced. The deformable element is then flexed by the eccentric. It is preferable for only pressure forces and substantially no friction forces to act at a contact surface of the eccentric and of the deformable element. A corresponding division of the eccentric into an inner region and a bearing ring is also possible if the eccentric is an external rotor arranged around an inner housing. It is also possible for the outer bearing ring to be dispensed with and for the rollers of the bearing to roll directly on or against the deformable element.
The pump preferably has at least one drive for the movement of the eccentric. The drive is preferably an electric motor connected to the eccentric by a shaft which runs along the axis. The pump is preferably also suitable for being operated in the opposite direction to the delivery direction. For this purpose, the eccentric is rotated counter to the delivery direction.
In the case of a pump of this type, an angular spacing between the inlet and the outlet in the circumferential direction about the axis, that is to say in particular the distance between those opening regions of the inlet and of the outlet furthest apart from one another across the inlet and the outlet, can be measured. The angular spacing is preferably delimited by the in each case outer regions, which are spaced apart to the maximum extent of the inlet and of the outlet. The angular spacing may therefore also be referred to as the maximum angular spacing of the inlet and of the outlet, or of the cross-sectional areas of the inlet and of the outlet. The angular spacing may furthermore be described by the angle of a circular arc segment, which is large enough to completely cover both the inlet and also the outlet.
Furthermore, an angular segment can likewise be measured which spans the seal in the circumferential direction and, in so doing, closes the delivery path. In particular, the angular segment thus relates to a section between two adjacent closed pump volumes. Here, the delivery path is closed in the angular segment owing to a deformation of the deformable element. In the angular segment of the delivery path, the delivery path has no open cross-sectional area. It is provided here that the angular segment is larger in terms of magnitude than the angular spacing. This leads, in particular, to the configuration in which, if the single seal is positioned centrally between the inlet and the outlet, those opening regions of the inlet and of the outlet which are situated furthest apart from one another are both and simultaneously still reliably closed by the seal. It is thus possible for undesired and/or simultaneous exertions of pressure by the inflowing liquid and/or the outflowing liquid to be reduced. It is likewise possible for the forces or energy for operating the pump to be kept permanently lower, and for an undesired positional displacement of the seal, and the possibly associated irregularities in spray pattern formation, as a result of pressure pulses to be considerably restricted. Furthermore, dosing accuracy is improved because undesired bypasses in the delivery path past the seal are reliably avoided even from the aspects of wear, high load and aging. It is accordingly preferable for the angular segment to be designed to be larger than the angular spacing by at least 5%, in particular by at least 8% and particularly preferably by at least 12%. Depending on the number of seals in the delivery path of the pump, it is expedient for the angular segment to be larger than the angular spacing by at most 120%, in order that an adequately large delivery volume (closed pump volume) can still be formed here.
The pump is particularly advantageous if the angular spacing between the inlet and the outlet is less than 40° [angular degrees]. It is preferable for the angular spacing to be less than 30° and in particular less than 25°, wherein, to ensure an adequate cross section of the inlet and of the outlet for use in the automotive sector, the angular spacing should possibly not fall (significantly) below 18°. A particularly small angular spacing makes it possible to realize a particularly compact pump with a particularly high delivery rate, because less space is required for the inlet and the outlet, and the at least one closed pump volume can be particularly large.
The pump is furthermore advantageous if the at least one inlet and the at least one outlet have a cross-sectional area which is elongate in the direction of the axis.
This refers to the cross-sectional area of inlet and outlet directly at the gap between eccentric and pump housing. The cross-sectional area of the inlet and of the outlet is passed over by the seal when the eccentric is rotated. Here, the seal rolls on the pump housing. An elongate cross-sectional area is preferably oval. By an elongate cross-sectional area in an axial direction, it is possible for the extent of the inlet and of the outlet in the circumferential direction to be reduced. This makes it possible for the angular spacing between the inlet and the outlet to be reduced. Even though a “symmetrical” design of the cross-sectional areas of the inlet and of the outlet is assumed here, it may likewise be expedient, in certain applications, for only the cross-sectional areas of the inlet or of the outlet to be designed in this way, or for both cross-sectional areas to be designed with a different manifestation of the elongate cross-sectional area (for example different lengths, widths, curvatures, etc.).
Furthermore, the pump is advantageous if the angular segment spanned by the seal is greater than 90° [angular degrees].
By such a large angular segment in which the seal is formed and the delivery path is closed, it is made possible for the pressure increase in the at least one closed pump volume, or the compression of the at least one closed pump volume, to be realized in a particularly effective manner. It is even particularly advantageous for the angular segment that is spanned to be greater than 120°. Here, the angular segment that is spanned should not exceed for example 180°, because otherwise the at least one closed pump volume becomes too small, and the delivery power of the pump would fall.
The pump is furthermore advantageous if the eccentric has a shape that deviates from the circular shape, such that a displacement of the at least one seal in the delivery direction from the inlet to the outlet gives rise to at least one of the following effects:
For the formation of the seal by the eccentric, the external shape of an eccentric is relevant. The shape of an eccentric can be described with the aid of a polar coordinate system, in which the pole of the coordinate system lies on the axis of the eccentric. In this coordinate system, an eccentric has a varying radius. Customary eccentrics for the pumps provided here are circular and arranged eccentrically with respect to the axis of the pump, such that a rotation of the eccentric about the axis gives rise to an eccentric movement of a circumferential surface. In the described polar coordinate system illustrated, the radius of an eccentric of this type varies over the circumference, or in the manner of a sinusoidal curve. This gives rise to a flat region, in which the radius of the eccentric is smaller than in an elevated region. The smallest radius of the eccentric in the polar coordinate system defines a circular basic shape of the eccentric. The circular basic shape is a circle concentric with respect to the axis and having the smallest radius of the eccentric in the polar coordinate system. The elevated region projects beyond the circular basic shape. The eccentric presses by way of the elevated region against the deformable element and thus generates the seal.
The eccentric with a non-circular shape may, for example be oval, or may have some other shape deviating from the circular shape. A non-circular eccentric may also be described in that the radius of an eccentric of this type, depicted over the circumference, has, in the polar coordinate system, a shape differing from a sinusoidal curve. In the case of an eccentric of this type, an elevated region may account for a greater angular fraction than a flat region. It is also possible that, in a delivery direction, a rising flank of the elevated region is steeper than a falling flank. Furthermore, multiple elevated and flat regions may be provided over the circumference.
A non-circular eccentric may also be equipped with a bearing that separates an outer bearing ring from an inner eccentric region. The bearing may be flexible and deformable rather than rigid and circular. Then, during the rotation of the inner eccentric region, the bearing deforms in each case correspondingly to the eccentric movement, and transmits said movement to the deformable element.
The two described effects may arise individually or in combination with one another. If the liquid delivered by the pump is compressible, or even (also) a gas is delivered instead of a liquid, then the closed pump volume in the delivery path is compressed. If the liquid delivered by the pump is incompressible, then a compression of the closed pump volume is not possible. Instead, it is then the case that the deformable element is deformed and/or compressed. During the compression, the deformable element is itself compacted. During a deformation, it is, for example, possible for regions of the deformable element to be elastically displaced. In the case of the delivery of liquids and gases with low compressibility, it is also possible for both effects to occur in parallel with one another. The compression and/or the pressure increase cause(s) pressure fluctuations during the delivery to be smoothed, and the delivery action to be made more homogeneous.
The pump is furthermore advantageous if the pump housing has a shape that deviates from the circular shape, such that a displacement of the at least one seal in the delivery direction from the inlet to the outlet gives rise to at least one of the following effects:
Such a design of the pump housing may be an alternative to the above-discussed design of the eccentric. It is generally simpler for the described advantageous effects to be achieved by way of a design of the pump housing rather than by way of the design of the eccentric. This is for example, owing to the fact that the pump housing is static and, by contrast to the eccentric, does not rotate. In this way, it is, for example, possible for a deformable bearing ring, such as has been described above, to be omitted.
The statements made for the eccentric with the aid of a polar coordinate system regarding the shape that deviates from the circular shape can also be transferred to a non-circular pump housing or a pump housing that deviates from the circular shape. Here, a deviation from a basic shape in the region of the static seal remains disregarded in each case. For the question of whether a pump housing is one with a circular shape or a non-circular shape, it is in particular only that region of the pump housing situated between the inlet and the outlet in the delivery direction that is of importance. A possible depression of the pump housing in the region of the static seal counter to the delivery direction between outlet and inlet is not taken into consideration here.
It is also possible for both the eccentric and the pump housing to have a shape that deviates from the circular shape, such that a displacement of the at least one seal in the delivery direction from the inlet to the outlet gives rise to at least one of the two described effects.
The pump is furthermore advantageous if at least the pump housing or the eccentric is configured such that an arcuate gap between the pump housing and the eccentric, in which arcuate gap the deformable element is arranged, tapers continuously in the delivery direction from the inlet to the outlet.
In the description of the tapering of the arcuate gap toward the outlet, it is to be taken into consideration that the eccentric is of eccentric form. The eccentricity is to be disregarded in the description of the tapering of the gap.
Rather, the gap is to be measured between the pump housing and the circular basic shape, defined further above, of the eccentric. The arcuate gap is a segment of a ring-shaped gap between the eccentric and the pump housing.
In the delivery direction from the inlet to the outlet, there is then progressively less space available in the arcuate gap for the deformable element and the at least one pump volume the further the at least one pump volume is displaced toward the outlet. In this way, a progressively more intense compression of the pump volume, and/or a progressively more intense deformation of the deformable element, occur(s) on the path toward the outlet. It is thus possible for the described effects of a compression of the pump volume or of an increase in the pressure in the closed pump volume to be achieved in a particularly effective manner.
The pump is furthermore advantageous if the pump housing has a first radius at the inlet and has a second radius at the outlet, wherein the first radius is smaller than the second radius, and the first radius transitions continuously into the second radius.
Such a design of the pump housing is a particularly simple variant for realizing a narrowing of the arcuate gap between the eccentric and the pump housing. The shape of the pump housing with a continuously decreasing radius may also be referred to as a (sectional) worm shape.
The described design of the pump housing and the described design of the eccentric can in each case also be used independently of the design of the inlet and of the outlet, with the angular spacing, and of the seal, with the spanned angular segment. Expressly also included in the description here are pumps in which the angular segment is not larger than the angular spacing, but in which the housing and/or the eccentric are/is configured such that, during a displacement of the at least one seal in the delivery direction from the inlet to the outlet, at least one of the following effects already described further above arises:
The pump is furthermore advantageous if at least one of the following components is designed such that, during the displacement of the at least one seal from the inlet to the outlet, a continuous adaptation of the pressure from the inlet to the outlet takes place within the pump as a result of the compression of the at least one closed pump volume or as a result of the pressure increase that occurs as a result of the deformation of the deformable element:
The inlet of the pump is normally connected to a suction line, via which the pump draws in liquid. The outlet of the pump is normally connected to a pressure line, via which pressurized liquid exits the pump. On the path of the liquid from the inlet to the outlet through the pump, the pressure is adapted preferably in continuous fashion from the pressure at the inlet to the pressure at the outlet. This is preferably achieved by way of at least one of the measures described further above. A continuous adaptation of the pressure from the inlet to the outlet makes it possible for undesired pressure peaks and pressure fluctuations to be prevented in a particularly effective manner.
Also proposed is a motor vehicle, comprising an internal combustion engine, an exhaust-gas treatment device for the purification of the exhaust gases of the internal combustion engine, and a device having a described pump, by which a liquid (in particular urea-water solution) for exhaust-gas purification can be delivered into the exhaust-gas treatment device. On the exhaust-gas treatment device there is preferably provided a metering device by which the liquid for exhaust-gas purification delivered by the pump can be fed to the exhaust-gas treatment device. The metering device, the pump and a tank for storing the liquid are preferably connected to one another by a line. In the exhaust-gas treatment device there is preferably provided an SCR catalytic converter at which nitrogen oxide compounds in the exhaust gas of the internal combustion engine are reduced with the aid of the liquid for exhaust-gas purification.
The invention and the technical field will be explained in more detail below on the basis of the figures. The figures show particularly preferred exemplary embodiments, to which the invention is however not restricted. In particular, it should be noted that the figures and, in particular, the illustrated proportions are merely schematic. In the drawings:
The pump 1 furthermore has a static seal 29 which prevents a backflow of liquid from the outlet 4 to the inlet 3 counter to the delivery direction 11. In
In all of the design variants of the pump 1 in
In all of the design variants illustrated in
In
For illustrative purposes, delivery of a compressible medium is shown in
Steps a) to e) show in each case five different positions of the eccentric 5, wherein the eccentric 5 is moved further in the delivery direction 11 from one step to the next.
It can be seen in
The pump housing 2 as per
By way of precaution, it should also be noted that the combinations of technical features shown in the figures are not generally binding. For example, technical features from one figure may be combined with other technical features from a further figure and/or from the general description. The only exception to this is if the combination of features has been explicitly referred to here and/or a person skilled in the art identifies that the basic functions of the device can no longer be realized otherwise.
Thus, while there have been shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2013 106 170.2 | Jun 2013 | DE | national |
This is a U.S. national stage of application No. PCT/EP2014/061546, filed on 4 Jun. 2014, which claims priority to the German Application No. DE 10 2013 106 170.2 filed 13 Jun. 2013, the content of both incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/061546 | 6/4/2014 | WO | 00 |
