Technical Field

[0001 ] The invention relates to a doser for injecting a liquid into an exhaust system of a combustion engine, and to a sealing ring for such a doser.

Background Art

[0002] Selective Catalytic Reduction (SCR) is a well-known technique to reduce environmentally harmful emissions of a combustion engine. Specifically, nitrogen oxides (NOx) are converted with the aid of a catalyst into Nitrogen (N2) and water. The reaction requires that a reductant, like anhydrous ammonia (NH3), aqueous ammonia (NH4OH), or a urea solution, is added to the exhaust gas. Depending on the type of reductant, carbon dioxide may also be produced. In motor vehicles like passenger cars or trucks, the reductant is injected into an exhaust system by an SCR doser, which is directly or indirectly connected to a reservoir of the reductant. The installation location of the doser and the operating conditions in this location lead to special requirements on various components of the doser. This pertains to protection from elevated temperatures, exhaust gases, humidity, and the reductant itself. Accordingly, various sealing components are used to protect sensitive components, in particular electrical components. Moreover, the doser usually comprises a water jacket that is part of a cooling circuit and protects it from overheating.

[0003] One known design provides that a solenoid for actuating a valve of the doser, along with other components like connector cables, is disposed in a metal housing, which in turn is partially overmolded with plastic. While the plastic should ideally be in direct contact with the metal housing, thereby providing a fluid-tight connection, this is in reality oftentimes not the case. For various reasons, in particular expansion and contraction due to temperature changes, there may be a minimal gap between the plastic and metal components, which opens a possible leak path for a fluid. This fluid may then reach electrical components, leading to corrosion and ultimately to a failure of the doser. Therefore, it is necessary to protect the gap by a sealing element, e.g., a PTFE ring that is placed between the gap and nozzle end of the doser. Furthermore, an additional sealing element, like an elastomer O-ring, is placed between the plastic component and a surrounding wall element, usually an inner wall of the water jacket. However, this setup with two sealing elements increases cost and complexity. Also, a PTFE element which is used due to its relative robustness under elevated temperatures, has insufficiently reliable sealing properties.

[0004] EP 2 871 339 A1 discloses a conventional fluid injector, which may be configured for use in a reductant delivery unit of an SCR system.

Technical Problem

[0005] It is thus an object of the present invention to provide improved means for protecting inner components of an SCR doser against corrosion.

General Description of the Invention

[0006] The present invention provides a doser according to claim 1.

[0007] The invention provides a doser for injecting a liquid into an exhaust system of a combustion engine, the doser extending axially along a doser axis from a proximal side to a distal side, which distal side faces the exhaust system in assembled state. The combustion engine may e.g., be a gasoline engine or a Diesel engine. In particular, this may be the traction engine of a road vehicle like e.g. a passenger car or a truck. However, other applications are not ruled out. The doser is adapted to inject a liquid into an exhaust system of the engine. This may refer to any part of the exhaust system, i.e., any component that receives exhaust gases from the engine, like an exhaust manifold or an exhaust pipe. In this context, it could also refer to an exhaust gas recirculation pipe. The liquid may in particular be a reactant for a Selective Catalytic Reduction (SCR) process, in which case the doser may also be referred to as an SCR doser.

[0008] The doser extends axially along a doser axis. The doser axis may correspond to a symmetry axis of the doser or at least of some of its components. Also, the doser axis generally corresponds to the general flow direction of the liquid through the doser. With respect to this doser axis, one can define a proximal side and a distal side. The distal side is facing the exhaust system when the doser is installed. In some embodiments, the distal side may also be referred to as the lower side and the proximal side be referred to as the upper side, but the invention is not limited to a specific orientation of the doser with respect to gravity.

[0009] The doser comprises an injection channel extending axially to an injection valve disposed on the distal side. Depending on the layout, the injection channel may extend along the entire length of the doser or only along a portion of the doser. The injection channel may be symmetric with respect to the doser axis. Either way, it extends to an injection valve that is disposed on the distal side. The injection valve controls the injection of liquid into the exhaust system. Normally, it comprises a valve seat and a valve member, which may be pressed against the valve seat to close the valve or may be lifted from the valve seat. It may comprise a spring element that acts directly or indirectly on the valve member to bias the valve member against the valve seat. As a rule, the valve is electromagnetically actuated via a solenoid that is disposed around the injection channel. The doser also comprises an outlet opening at a distal side of the injection channel. When the injection valve is open, liquid flows through the injection channel and is ejected through the outlet opening.

[0010] Further, the doser comprises a wall element extending axially and circumferentially around the doser axis. Normally, the wall element is symmetric with respect to the doser axis. It may at least partially be cylindrical and/or frusto-conical. Normally, it is made of metal, like stainless steel, but it could be made of a different material. It could be part of an outer wall of the doser, but it could also be some inner wall, as will be explained below.

[0011 ] The doser also comprises a composite body disposed radially inside of the wall element and at least partially spaced therefrom, which composite body comprises a metal component and a plastic component wherein a cover portion of the plastic component extends radially outwards from a first portion of the metal component, and wherein a second portion of the metal component extends distally from the first portion beyond the plastic component. The name “composite body” simply refers to the two elements made of different materials that the composite body comprises. The composite body may be part of a solenoid assembly that comprises the above-mentioned solenoid. In some embodiments, the composite body also comprises the solenoid and may be referred to as a solenoid body or the like. In general, it is disposed radially inside of the wall element. In other words, the wall element is disposed radially outside of the composite body (i.e. , further away from the doser axis).

[0012] The composite body, as well as the metal element and the plastic element, can be symmetric about the doser axis. The metal component is of course made of metal, normally steel. It could be made of hot or cold formed sheet metal or cast metal. The plastic component can in general be made of any type of plastic material, normally a plastic material that is suited for injection molding. Consequently, the plastic component is normally injection molded. The plastic component comprises a cover portion that extends radially wards from a first portion of the metal component, thereby covering it from the outside. Preferably, the cover portion is disposed at least adjacent the first portion. A minimal distance between the cover portion and the first portion is normally less than 0.5 mm. More preferably, the cover portion is in contact with the first portion. Anyway, in the respective region, the first portion of the cover portion form a two-layer structure in the radial direction. A second portion of the metal component extends distally from the first portion beyond the plastic component. The first portion and second portion are portions of the metal component and thus are connected. While the first portion is covered by the cover portion of the plastic component, the second portion extends in the distal direction beyond the plastic component. Accordingly, it is not covered by any part of the plastic component. In this region, there is only a single-layer structure formed by the second portion of the metal component. As a rule, both the cover portion and the second portion are at least partially spaced from the wall element in the radial direction.

[0013] The doser further comprises a sealing ring made of an elastomeric material and being disposed between the composite body and the inner wall, wherein the sealing ring comprises a first sealing portion sealingly disposed between the inner wall and the second portion, a second sealing portion sealingly disposed between the inner wall and the cover portion, and an intermediate portion axially interposed between the sealing portions. The elastomeric material may in particular be a fluorocarbon-based fluoroelastomer like FKM, or HNBR (hydrogenated nitrile butadiene rubber). The function of the sealing ring is to prevent potentially harmful substances, like exhaust gases and/or the liquid that is injected into the exhaust system, from entering into the inner parts of the doser. In particular, electric components inside the composite body need to be protected. Specifically, two potential leak paths are sealed by the seal ring. The first leak path would be between the composite body and the wall element. This leak path is closed by the second sealing portion, which sealingly engages the cover portion of the plastic component and the wall element. The sealing effect of the sealing ring should at least be fluid-tight and optionally gas-tight. The second leak path would be between the first portion and the cover portion. This second leak path is closed by the first sealing portion, which sealingly engages the wall element and the second portion. Since, by definition, the second portion extends distally from the first portion, the first sealing portion creates a sealing barrier distal from the first portion and the cover portion. Accordingly, since any harmful substances would enter the doser from the distal side where the outlet opening is disposed, such substances are prevented from passing through any of the above- mentioned leak paths. While the first sealing portion and the second sealing portion each have an individual sealing function, they are both parts of a single sealing ring and are connected by an interposed intermediate portion. The intermediate portion is interposed between the sealing portions with respect to the axial direction. On the one hand, combining both sealing portions in a single sealing ring reduces the number of components and facilitates assembly of the doser. On the other hand, due to the connection of the sealing portions, at least one sealing portion may mechanically stabilize the other sealing portion. In other words, a sealing portion can have a shape that would be unstable on its own but is stabilized by the connection to the other sealing portion.

Remarkably, the intermediate portion is radially recessed with respect to both sealing portions, whereby a recess is partially defined between the sealing portions and the intermediate portion. Specifically, the intermediate portion is recessed radially inwards and/or outwards with respect to both sealing portions, whereby a recess is formed with respect to the wall element and/or with respect to the composite body. Thanks to this feature, the two sealing portions can better be deformed individually, which enhances the sealing effect towards the wall element, resp. composite body.

[0014] In a preferred embodiment, the second portion is radially recessed with respect to the cover portion, and the first sealing portion extends radially further inwards than the second sealing portion. In this embodiment, the cover portion extends further in the radial direction than the second portion. In some embodiments, the first portion and the second portion are in the same radial position, wherefore the cover portion has to extend further and the radial direction. In this embodiment, the second portion and the cover portion may form a step. Consequently, since the first sealing portion is in contact with the second portion while the second sealing portion is in contact with the cover portion, the first sealing portion needs to extend radially further inwards. In this embodiment, the cross-section of the sealing ring may sometimes be described as generally L-shaped.

[0015] Preferably, the plastic component is overmolded over the metal component, wherein a boundary surface between the cover portion and the first portion extends proximally from an end region adjacent the second portion. The overmolding process represents an easy way to establish a tight connection between the plastic component and the metal component. At the same time, the plastic component can be overmolded over at least one electrical component, like a solenoid and/or an electrical connection. Ideally, the connection between the plastic component and the metal component could be at least fluid-tight, so that the above-mentioned second leak path should be closed. However, the connection is often not tight under operating conditions, mostly due to thermal expansion and contraction. A boundary surface or boundary area, in which the plastic component and the metal component are either in contact with each other or in close proximity to each other, extends from an end region adjacent the second portion in the proximal direction with respect to the doser axis. At least a portion of the boundary surface could represent the second leak path, while the end region is a possible entrance point for the second leak path. However, the inventive design of the seal ring with the first sealing portion prevents harmful substances from entering through this entrance point.

[0016] One embodiment provides that the wall element is an inner wall of a water jacket for a cooling liquid. The cooling liquid is normally water or a water-glycol mixture. The water jacket is connected to a cooling circuit through which “fresh” cooling liquid can be introduced into the water jacket, while “used” cooling liquid can be extracted. Normally, the doser needs a water jacket to prevent it from overheating in the proximity of the exhaust system. The water jacket may also be symmetric with respect to the doser axis. The inner wall is a wall element that delimits the water jacket on the radially inner side. This inner wall, as well as other wall elements of the water jacket, are usually made of metal, e.g., stainless steel or an aluminum alloy.

[0017] Although the sealing function on the distal side is preferably performed exclusively by the sealing ring, an additional element may be necessary, since the sealing ring is normally a poor heat conductor. Preferably, the doser comprises an annular heattransfer element disposed between the composite body and the wall element and distally from the sealing ring. The heat-transfer element is adapted to transfer heat from the composite body to the wall element, in particular if the wall element is an inner wall of a water jacket. It is understood that the heat-transfer element is made of at least one material that has a rather high heat conductivity, normally at least 10 W/mK. In particular, the heat-transfer element may be made of graphite, which typically has a heat conductivity of at least 25 W/mK. Depending on the geometry of the heat-transfer element, the composite body and the wall element, the heat-transfer element may also provide some sealing function. However, it is normally not suitable to provide a sufficiently tight seal. It may, however, protect the sealing ring from hot gases and/or infrared radiation. Contrary to prior art, however, there is no need for an additional sealing element distal from the heat-transfer element. Rather, a distal cavity may be disposed on a distal side of the heattransfer element, which distal cavity is in communication with the outside of the doser. Accordingly, gas and/or liquids from the outside of the doser can enter the distal cavity. As a rule, these can get past the heat-transfer element but are blocked by the sealing ring, specifically the first sealing portion thereof.

[0018] Typically, the intermediate portion is recessed radially inwards with respect to both sealing portions, so that a first recess is formed between the sealing portions, the intermediate portion and the wall element. In this embodiment, both sealing portions extend further radially outwards than the intermediate portion. This pertains especially to the undeformed state of the sealing ring. When the sealing ring is installed in the doser, both sealing portions are usually deformed, wherefore the difference between the radial extension of the sealing portions and the intermediate portion may be smaller, but still be present. This design may facilitate individual deformation of the sealing portions towards the radial outside.

[0019] Alternatively or additionally, the intermediate portion is recessed radially outwards with respect to both sealing portions, so that a second recess is formed between the sealing portions, the intermediate portion and the composite body. In other words, both sealing portions extend further radially inwards than the intermediate portion. This pertains especially to the undeformed state of the sealing ring, but also to its installed state. This design may facilitate individual deformation of the sealing portions towards the radial inside. If the intermediate portion is recessed both radially inwards and outwards, it forms a kind of “wasp waist” of the cross section, with both sealing portions being wider in the radial direction.

[0020] According to one embodiment, the first sealing portion has a maximum first axial length and a maximum first radial width, which is greater than the maximum first axial length. As a rule, neither the axial dimension nor the radial dimension of the first sealing portion is constant for every part of it. In this context, the maximum first axial length represents the maximum radial dimension of the first sealing portion and the maximum first radial width represents its maximum radial dimension. It should be understood that the radial width does not correspond to a diameter of the first sealing portion, which is annular like the entire sealing ring and therefore has a central void. Rather, this is the radial distance between the innermost point of the first sealing portion and its outermost point. This embodiment represents a first sealing portion that is rather short in the axial direction and rather wide in the radial direction.

[0021 ] One embodiment provides that, in an undeformed state of the sealing ring, the ratio between the maximum first radial width and the maximum first axial length is between 3 and 6. It will be understood that when the sealing ring is installed in the doser, its dimensions change due to elastic deformation. Thus, any reference to the “undeformed state” indicates that the dimensions in the doser are usually different, although they may be the same. In this embodiment, the cross-section of the first sealing portion is considerably wider in the axial direction than in the axial direction, namely 3 to 6 times. This corresponds to a disc-like shape of the first sealing portion, wherein “disc” of course refers to an annular disc. It has been found that such a shape, which is normally prone to instability, can be stabilized due to the connection with the second sealing portion via the intermediate portion. Especially, but not exclusively, in this embodiment, the first sealing portion may comprise parallel proximal and distal side surfaces that are perpendicular to the axial direction.

[0022] Also, the second sealing portion can have a maximum second radial width that is smaller than the maximum first radial width. This is mostly the case if the second portion is radially recessed with respect to the cover portion as describe above. While the shape of the first sealing portion can be elongate in the radial direction, the dimensions of the second sealing portion in the radial and axial direction can be similar (or even identical).

[0023] Specifically, in an undeformed state of the sealing ring, the ratio between the maximum first radial width and the maximum second radial width can be between 1.5 and 4, preferably between 1.7 and 3.

[0024] As mentioned above, the intermediate portion may be the “wasp waist” of the cross-section. Correspondingly, the intermediate portion may have a minimum third radial width that is smaller than both the maximum first radial width and the maximum second radial width. Although the maximum first and maximum second radial width refer to the largest radial dimension, the minimum third radial width refers to the smallest radial dimension of the intermediate portion.

[0025] In particular, in an undeformed state of the sealing ring, the ratio between the maximum first radial width and the minimum third radial width can be between 4 and 10. In installed state, the ration is normally somewhat smaller than in undeformed state, but in the same order of magnitude.

[0026] In an undeformed state of the sealing ring, the ratio between the maximum first radial width and a total axial length of the sealing ring can be between 0.5 and 2. The ratio could in particular be between 0.8 and 1.5. If the ratio is significantly smaller, the sealing ring is relatively long in the axial direction, which may negatively affect its stability. If the ratio is significantly higher, the sealing ring is relatively short in the axial direction, which may make it difficult to properly define its abovementioned three portions.

[0027] All these terms have been explained above with respect to the inventive doser and therefore will not be explained again. Preferred embodiments of the inventive sealing ring correspond to those of the inventive doser.

Brief Description of the Drawings [0028] Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig.1 is sectional view of an inventive doser;

Fig.2 is a detail view of Fig.1 ;

Fig.3 is a perspective view of a seal ring of the doser of fig.1 ;

Fig.4 is a sectional view of the seal ring of fig.3; and

Fig.5 is a sectional view of a doser according to prior art.

Description of Preferred Embodiments

[0029] Figs.1 and 2 show an inventive doser 1 , specifically an SCR doser that is used for injecting a liquid reactant into an exhaust system (not shown) of a combustion engine. As is known, the liquid reactant may generally be a reductant agent comprising nitrogen, e.g. an aqueous solution of urea (known as AdBlue) or the like. The doser 1 is mostly symmetric to a doser axis A that defines an axial direction as well as a corresponding radial direction and tangential direction. It comprises an injection channel 2 that extends from a proximal side P to a distal side D, which faces the exhaust system in assembled state. A proximal O-ring 18 prevents liquid from the injection channel 2 from entering into the inside of the doser 1, where it could potentially lead to damage. At the distal side D of the injection channel 2, a valve 3 is disposed, which comprises a valve member 4 that rests against a valve seat 5. It is biased against the valve seat 5 by a spring element 6. In order to open the valve 3 and eject liquid through an outlet opening 10, a solenoid 7 can be activated which generates a magnetic field that lifts the valve element 4 from the valve seat 5, thus overcoming the action of the spring element 6.

[0030] The solenoid 7 is integrated into a composite body 15, which comprises metal parts as well as a plastic component 17 that is overmolded onto the metal parts. Specifically, a metal component 16, which is roughly cylindrical and symmetric about the doser axis A, is overmolded by the plastic component 17. Towards the distal side D, a first portion 16.1 of the metal component 16 is overmolded and covered by a cover portion 17.1 of the plastic component 17, while a second portion 16.2 distally extends from the first portion 16.1 and beyond the plastic component 17. The composite body 15 as a whole is disposed radially inside of a wall element 11 of a water jacket 8, which is hereinafter referred to as inner wall 11. The water jacket 8 is necessary to cool the doser 1 during operation of the exhaust system. Radially on its outside, the water jacket 8 is delimited by an outer wall 9, which also forms an outer housing of the doser 1 as a whole. As can clearly be seen in fig. 1 and 2, the composite body 15 is radially spaced from the inner wall 11. An annular gap 13 is formed at a distal end of the inner wall 11. A distal end cavity 14 inside the inner wall 11 communicates with the outlet opening 10 through the gap 13. Accordingly, exhaust gases as well as components of the reactant liquid could enter through the gap 13 and possibly pose a threat to electric components like the solenoid 7 or electrical connections (not shown). A first potential leak path is between the composite body 15 and the inner wall 11. A second potential leak path is between the metal component 16 and the plastic component 17. Although the plastic component 17 is overmolded, there may be small, even microscopic, gaps along a boundary surface 26 between the plastic component 17 and the metal component 16. Potentially corrosive substances could enter into these gaps through an annular end region 27 adjacent the second region 16.2.

[0031 ] Both of these leak paths are closed by a single sealing ring 20 made of an elastomeric material like FKM or NHBR. The cross-section of the sealing ring 20 can be described as roughly L -shaped. It comprises a first sealing portion 20.1 that is sealingly disposed between the inner wall 11 and the second portion 16.2, and a second sealing portion 20.2 that is sealingly disposed between the inner wall 11 and the cover portion

17.1. The above-mentioned first leak path is mainly blocked by the second sealing portion

20.2, while the second leak path is blocked by the first sealing portion 20.1. Both sealing portions 20.1 20.2 are connected by an intermediate portion 20.3. While the figs. 1 and 2 show the sealing ring 20 in a deformed state, figs. 3 and 4 show an undeformed state.

[0032] The first sealing portion 20.1 has a maximum first axial length L1 and a maximum first radial width R1, which is greater than the maximum first axial length L1. Specifically, in the undeformed state of the sealing ring 20, the ratio between the maximum first radial width R1 and the maximum first axial length L1 can be between 3 and 6, in this example it is approximately 4.6. The first sealing portion has proximal and distal side surfaces 20.4, which are parallel to each other and perpendicular to the axial direction. The second sealing portion 20.2 has a maximum second radial width R2 that is smaller than the maximum first radial width R1. In the undeformed state, the ratio between the maximum first radial width R1 and the maximum second radial width R2 can be between 1.5 and 4, in this example it is approximately 2.0. A minimum third radial width R3 of the intermediate portion 20.3 is smaller than both the maximum first radial width R1 and the maximum second radial width R2. The ratio between the maximum first radial width R1 and the third radial width R3, in this example, is approximately 7.4, but could e.g., be between 4 and 10. The ratio between the maximum first radial width R1 and a total axial length L of the sealing ring is approximately 1.1, but could be e.g., between 0.5 and 2. It will be understood that all the ratios specified for the undeformed state are usually somewhat different in the installed state, in which the sealing ring 20 is elastically deformed.

[0033] The intermediate portion 20.3 is recessed radially inwards with respect to both sealing portions 20.1, 20.2, so that a first recess 22 is formed between the sealing portions 20.1, 20.2, the intermediate portion 20.3 and the inner wall 11. Likewise, the intermediate portion 20.3 is recessed radially outwards with respect to both sealing portions 20.1, 20.2, so that a second recess 23 is formed between the sealing portions 20.1 20.2, the intermediate portion 20.3 and the composite body 15. On the one hand, the design of the sealing ring 20 allows for a certain degree of individual deformation of each sealing portion 20.1 20.2. On the other hand, the connection via the intermediate portion 20.3 may help to stabilize at least one of the sealing portions 20.1 20.2. This is especially true for the first sealing portion 20.1 , which is rather thin along the axial direction and therefore could undergo excessive deformation if it wasn’t connected to the second sealing portion 20.2 through the intermediate portion 20.3. Such excessive deformation could lead to a loss of its sealing properties.

[0034] An annular heat-transfer element 21 made of graphite is disposed between the inner wall 11 and the composite body 15 distally from the sealing ring 20. Main function of the heat-transfer element 21 is to transfer heat to the inner wall 11 and thus to the water jacket 8. Additionally, it has limited sealing properties, but it should be understood that these would be insufficient to prevent oxidizing substances from reaching 1 of the above-mentioned leak paths. In other words, the actual sealing function is exclusively performed by the sealing ring 20. The single sealing ring 20 has proven effective for protecting the inside of the doser, especially its electric components, from potentially harmful substances.

[0035] For comparison, fig. 5 shows a doser 1 according to prior art. The doser 1 and its components are mostly identical to the inventive doser 1 shown in fig. 1 and 2 and insofar will not be described again. However, instead of the L-shaped sealing ring 20, a distal O-ring 24 is disposed between the plastic component 17 and the inner wall 11. In its undeformed state, the cross-section of the O-ring 24 is circular, whereas in the installed state of fig. 5, it is roughly elliptical. It will be understood that this O-ring 24 may be adequate for blocking the above-mentioned first leak path, but is totally unsuited for blocking the second leak path between the metal components 16 and the plastic component 17. Accordingly, a secondary seal 25 is provided distally of the heat-transfer element 21 in order to supplement the sealing function of the O-ring 24. Due to its proximity to the exhaust system, the secondary seal 25 cannot be made of an elastomeric material, but is made of PTFE, which has less favorable sealing properties. Accordingly, intrusion of harmful substances through the second leak path cannot be prevented. Also, the design shown in fig. 5 needs to separate sealing elements 24, 25, while the inventive design achieves a better sealing performance with a single sealing ring 20.

Legend of Reference Numbers:

1 doser

2 injection channel

3 injection valve

4 valve element

5 valve seat

6 spring

7 solenoid

8 water jacket

9 outer wall

10 outlet opening

11 inner wall

13 gap

14 distal cavity

15 composite body

16 metal component

16.1 first region

16.2 second region

17 plastic component

17.1 cover portion

18 proximal O-ring

20 sealing ring

20.1 , 20.2 sealing portion

20.3 intermediate portion

20.4 side surface

21 heat-transfer element

22, 23 recess 24 distal O-ring

25 secondary seal

26 boundary surface

27 end region

A doser axis

D distal side

L, L1 axial length

P proximal side

R1 , R2, R3 radial width