TECHNICAL FIELD

The present invention relates to a reducing agent filter device, reducing agent dosing unit, reducing agent dosing system and a vehicle comprising the filter device of the type as defined in the appended claims and the description below.

BACKGROUND ART

Vehicles comprising an internal combustion engine and especially a diesel engine usually comprise a reducing agent feeding system arranged to transport a urea-containing solution, such as commercially available Adblue ^® , from a urea-solution tank to a selective catalytic reduction (SCR)-system in an exhaust gas system of the vehicle. The reducing agent system usually comprises at least one filter device for removal of particulate matter from the reducing agent before it reaches injection system components. The injection system components, such as pumps, are sensitive to impurities. Thus, filtration of particulate matter from the reducing agent is essential to avoid operational disturbances.

The environmental demands continue to be strict, which means that effective exhaust gas purification systems need to be provided. However, the space in the vehicles is limited. Also, the weight of the components should not increase the total weight of the vehicle. Thus, reducing agent dosing systems including the tank need to be placed in a compact manner. This in turn may require limitation of the volume for filter devices. Therefore, two or more compact filter devices have been provided in feeding lines transporting reducing agent from the tank to the injection system. However, these filter devices are often small and have a small filtration area or volume and are thus not sufficiently effective. Further, they are often placed in a manner which makes them difficult to reach, e.g. in a tank, which in turn can be placed in a narrow and inaccessible space. Thus, the filters are complicated to change and clean while they are essential to ensure the operation of the SCR-system. Therefore, there is a need to eliminate the need for tank filters while the filtering efficiency is not impaired. Also, there is a need to provide filter devices with a compact and light-weight design. Further, there is a need to facilitate the service of the filtering devices. There have been attempts in the prior art to improve liquid filter devices in a vehicle. For example US2015198071A1 discloses a urea dosing system including several filters, two of which can be integrated with pump housing. However, the problem of providing effective filtration while having an easy access to filters per se still exists.

Therefore, there is still a need to improve the filtering devices in the field.

SUMMARY OF THE INVENTION

The objective of the present invention is to provide a reducing agent filter device, which has an improved filtering capacity. It is also an objective to provide a reducing agent filter device which is compact and space saving and has a simple and light construction. Further, it is an objective of the present invention to minimize the problems with operational disturbances in a reducing agent system and thus exhaust gas purification system of a vehicle.

It is also an objective of the present invention to provide a reducing agent filter device (also referred to as filter device herein), dosing unit and a dosing system eliminating the need for further filter devices upstream of the filter device. For example it is an objective to eliminate the need for filter elements in the reducing agent tank.

Further, it is an objective to provide a reducing agent dosing unit which is space-saving and which comprises a filter device which can be easily served and which has filter elements which can be easily changed.

Also, it is an objective of the present invention to provide a reducing agent dosing system and/or an exhaust gas system with a space saving, robust and light construction with a decreased amount of components.

Further, it is an objective to provide a vehicle having the advantages above.

These objectives are achieved with a reducing agent filter device, reducing agent dosing unit, reducing agent dosing system and vehicle of the type specified by the features of the appended claims.

The present invention thus relates to a reducing agent filter device comprising an inner filter unit comprising a first filter element of a first filter material and a second filter element of a second filter material. The first filter element and the second filter element extend in an axial direction (X) and a direction perpendicular to the axial direction (D) of the filter device. The second filter element is arranged coaxially with the first filter element and such that the first filter element surrounds the second filter element. The second filter element constitutes a hollow central tube of the reducing agent filter device. The reducing agent filter device further comprises an outer filter unit comprising a third filter element, which at least partially surrounds the inner filter unit. By arranging the filter device with the inner and the outer filter units, a construction allowing service and exchange of filter elements separately is obtained. Further, a compact and effective filtering device for the reducing agent is achieved and thus it is possible to minimize problems with operational disturbances. Further, the first, second and third filter elements are located in the filter device, whereby a space saving construction is obtained. Also, the filter device of the present disclosure maximizes the filtering efficiency, since the first and the second filter element can capture particulate material that passes the third filter element. Also, a filter element or device in a reducing agent tank is not necessary, since the third filter element can replace the filter element which otherwise would be placed in the tank. Also, by the filter device of the present invention it can be assured that particulate material will be captured in the filter device, and the amount of particulate material entering additional components downstream of the filter device in a liquid feeding system is minimized.

The third filter element may be arranged coaxially with the first filter element and the second filter element of the inner filter unit. In this way a compact and light weight structure for the filter device can be obtained.

The filter device may have a substantially circular cylindrical shape. The outer filter unit surrounds the inner filter unit. By arranging the device with a circular cylindrical shape, a symmetrical shape for the filter device is obtained, whereby the filter materials can be equally loaded over the surface and/or volume of the filter elements. Thus, the operational lifetime of the filter elements can be prolonged.

According to one variant, the first filter material may comprise nylon fibres or is paper-based. The first filter material may have a mesh size of less than or equal to 25 pm. In this way fine particulate material can be captured. The second filter material may comprise a plastic or metallic net. The second filter material may have a mesh size of less than or equal to 30 pm. In this way the particulate matter which has passed the third and the first filter elements may be captured and the filtering efficiency may be further improved. The third filter material may comprise a plastic or metallic net, nylon fibres or is paper-based and may have a mesh size of less than or equal to 75 pm, preferably 70 pm. In this way, also coarser particles can be captured while the risk for clogging of the third filter element is decreased.

The filter device may further comprise a housing which surrounds the outer filter unit. The housing protects the filter units and provides an integrated structure in a compact manner. The housing may comprise a light weight material, such as plastic or aluminium. An insulation layer may be arranged between the housing and the third filter element. Suitably, the insulation layer and the third filter element are arranged at a distance from each other in a direction perpendicular to the axial direction (X) of the device. The insulation layer protects the third filter element mechanically and provides protection against temperature variations, such as freezing.

An enclosure may be arranged to surround the inner filter unit in a liquid tight manner. In this way it is for example possible to place a pump device between the outer and the inner filter unit and in this way to separate the vacuum and the pressure side of the filter device. Suitably, the enclosure is arranged at a distance from the first and the third filter elements in a direction perpendicular to the axial direction of the device, whereby liquid flow between the enclosure and the filter elements is enabled. The enclosure may be made of a material which is heat conducting, such as metal. In this way temperature of the inner filter unit can be easily adapted to the temperature of the outer filter unit. A foam material element may be arranged inside the hollow central tube. In this way expansion of the liquid caused by freezing can be controlled. The foam material element may be surrounded by protective plastic layer, such as EPDM, whereby the foam material protected. The housing may comprise a re-openable cover means comprising liquid inlet and outlet openings. Thus, the filter units inside the housing can be protected.

The reducing agent filter device may comprise liquid pathways in which the reducing agent is arranged to flow first through the third filter element, secondly through the first filter element and thirdly through the second filter element. In this way the filter device obtains a compact construction.

The present invention further relates to a reducing agent dosing unit comprising the reducing agent filter device as described above and a pump device arranged downstream of the outer filter unit and upstream of the of the inner filter unit. Further, the present invention relates to reducing agent dosing system for an exhaust gas system of an internal combustion engine. The reducing agent dosing system comprises a tank for the reducing agent, the reducing agent dosing unit as described above and an injection device arranged to inject the reducing agent from the filter device into the exhaust gas system. The reducing agent dosing system may comprise a first pressure sensor arranged to detect the reducing agent pressure downstream of the reducing agent filter device. In this way the flow pressure of the reducing agent may be checked and e.g. clogging may be detected if the pressure is lower than a pre-determined pressure. The system may optionally comprise a second pressure sensor arranged to detect the reducing agent pressure upstream of the reducing agent filter device. In this way pressure difference between the upstream position and the downstream position in respect of the filter device can be detected. Further, the system may comprise a third pressure sensor arranged downstream of the third filter element and upstream of the pump. In this way clogging of the third filter element or the first and/or second filter element can be detected in an easy way.

Also, the present invention relates to a vehicle comprising the reducing agent filter device as described above, the reducing agent dosing unit as described above, and/or the reducing agent dosing system as de.

Further features and advantages of the present invention will be described in more detail in the detailed description below with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a schematic side view of a vehicle, which comprises a reducing agent filter device, reducing agent dosing unit and reducing agent dosing system for an internal combustion engine according to the present invention,

Fig. 2 shows in a coupling scheme for a urea dosing system comprising a urea dosing unit according to one aspect of the invention, and

Fig. 3 shows schematically a side cut of a reducing agent filter device according to one aspect of the invention, wherein arrows showing schematically the flow of fluid inside the filter device are provided.

DETAILED DESCRIPTION

Internal combustion engines are used in various types of applications and vehicles today, e.g. in heavy vehicles such as trucks or buses, in cars, motorboats, steamers, ferries or ships. They may also be used in industrial engines and/or engine-powered industrial robots, power plants, e.g. electric power plants provided with a diesel generator, and in locomotives. Due to strict regulations in respect of emissions, exhaust gases from the internal combustion engines need to be purified. Therefore, vehicles are provided with an exhaust gas purification system, also referred to as an exhaust system, which may comprise several components.

In connection with vehicles, the exhaust system may be partly or completely comprised in a silencer of a vehicle. Generally, the exhaust system may comprise one or more of the following components. Firstly, the silencer is usually equipped with an inlet for leading an exhaust gas flow into the silencer. The silencer may comprise a diesel oxidation catalyst (DOC) which may be arranged downstream of the inlet. A DOC is a unit designed to oxidize carbon monoxide, gas phase hydrocarbons and soluble organic fraction (SOF) of diesel particulate matter to C0 ₂ and H ₂ 0. A diesel particulate filter (DPF) may be arranged downstream of the DOC. A DPF is a unit designed to remove diesel particulate matter or soot from the exhaust gas flow. The DPF can for example be a catalysed soot filter (CSF). Further, a selective catalytic reduction (SCR) purification system comprising a dosing system for adding a reducing agent to the exhaust gas flow in order to reduce NO _x contents of the exhaust gas flow is arranged in the exhaust system. The reducing agent may be for example a urea-containing solution, such as a mixture containing water and urea, e.g. a product with the trade name AdBlue ^® . A mixing and vaporisation arrangement, which comprises a vaporisation chamber for mixing of the exhaust gas flow and reducing agent and for vaporization of the reducing agent is arranged downstream of the dosing system for the reducing agent. The SCR purification system comprises a SCR-substrate which may comprise vanadium, iron or copper catalyst, which breaks NO _x down to water vapour and nitrogen.

Further, an ammonia slip catalyst (ASC), which is designed to convert the NH ₃ slip to N ₂ and H2O, may be arranged downstream of the SCR purification system. An outlet for leading the exhaust gas flow out from the silencer is arranged downstream of the ASC. The silencer may comprise several outlets.

Generally, reducing agent dosing systems include a tank for the reducing agent, at least one filter and a pump to supply the reducing agent to the vaporization chamber in the exhaust gas system of a vehicle. The reducing agent may be for example injected to the vaporization chamber by means of an injection device. The components downstream of the filter device are usually sensitive for impurities and therefore effective reduction of particulate matter is needed to avoid operational disturbances. Due to lack of space in vehicles, a compact construction of the exhaust gas system is essential. Thus, it is important to utilize all space provided in the vehicle, also spaces which are not easy to access during service occasions. Therefore, for example reducing agent tank may be placed in a position which is not easy to reach. Therefore, the tank should have as few components as possible which require regular service or control to avoid service which is time consuming. Thus, there is a need for a reliable reducing agent filter device which is easy to serve and maintain. The present filter device solves these problems.

The filter device, dosing unit, dosing system and vehicle according to the present disclosure are now further described with reference to the appended drawings.

Fig. 1 depicts a vehicle 1 in a schematic side view which is provided with an internal combustion engine 2 that powers the vehicle's tractive wheels 4 via a gearbox 6 and a propeller shaft 8. The engine 2 is provided with an exhaust gas system 10 which is part of a silencer 12. The exhaust gas system 10 includes a SCR purification system (not shown) and is fluidly connected to a reducing agent tank 20, from which the reducing agent is supplied to the SCR purification system via a dosing system 24 comprising a dosing unit 22. The dosing unit 22 comprises a reducing agent filter device 23 (see Fig. 2) of the present invention and a pump 21 (see Fig. 2), which is arranged to feed the reducing agent further in the exhaust system. The engine 2 is powered by fuel 14 supplied to it via a fuel system 16 comprising a fuel tank 18.

A reducing agent dosing system 24 including a reducing agent dosing unit 22 is shown schematically in Fig. 2. The reducing agent dosing system 24 comprises a reducing agent tank 20 and the reducing agent dosing unit 22 comprising a pump device 21 arranged to pump the reducing agent from the tank 20, and a reducing agent filter device 23 comprising three filter elements 30, 26 and 28 in a housing 40. The reducing agent filter device 23 is arranged in fluid connection with the tank 20 comprising the reducing agent, e.g. AdBlue ^® , by means of the supply pump 21. The first filter element 26 and the second filter element 28 are located downstream of the pump 21 and thus on the pressurized side of the pump and the third filter element is located upstream of the pump 21 and thus on the vacuum side of the pump.

The filter device 23 comprises an inner filter unit 27 comprising a first filter element 26 and a second filter element 28. The reducing agent filter device 23 also comprises an outer filter unit comprising a third filter element 30. The inner and the outer filter units 27, 29 are arranged in the housing 40. The structure of the filter device is described more in detail in connection with Fig. 3. Preferably, the reducing agent filter device 23 is an independently attachable or detachable unit. Thus, the reducing agent filter device 23 may comprise detachable attachment means (not shown) that enable attachment and detachment of the unit to pipelines in the dosing system 24 in an easy way. Also, the filter device 23 and the pump device 21 may be detachably arranged to the pump 21 in the dosing unit 22, whereby easy maintenance and service can be performed. In this way a modular dosing unit with a reducing agent filter device 23 having exchangeable filter elements 26, 28 and 30 is provided. The housing 40 can be manufactured of any suitable material that tolerates the environment in an exhaust gas system of a vehicle and may comprise plastic material and/or metal, such as aluminium. The reducing agent dosing system 24 may comprise at least one additional component downstream of the reducing agent dosing unit 22. For example, an injection device 60 can be arranged downstream of the dosing system to inject the reducing agent into the exhaust gas system. Suitably, the injection device provides the reducing agent into the exhaust gas flow in a vaporization chamber of a SCR system, whereby the NO _x -content of the exhaust gas flow can be reduced. The injection device 60 may comprise an additional filter 62 to further protect the injection device from particulate impurities.

An embodiment of the reducing agent filter device 23 is schematically shown in Fig. 3 in an axial cut. The reducing agent filter device 23 comprises an inner filter unit 27 comprising a first filter element 26 of a first filter material and a second filter element 28 of a second filter material. The first filter material may comprise nylon fibres or is paper-based and may have a mesh size of less than or equal to 25 pm. The second filter material may comprise a plastic or metallic net and may have a mesh size of less than or equal to 30 pm. The reducing agent filter device 23 further comprises an outer filter unit 29, which comprises a third filter element 30, which at least partially surrounds the inner filter unit 27. The third filter material may comprise a plastic or metallic net, nylon fibres or is paper-based and has a mesh size of less than or equal to 75 pm, preferably 70 pm. The filter device 23 further comprises a housing 40 which surrounds the outer filter unit 29 and protects the filter elements against outside forces.

As further shown in Fig. 3, an insulation layer 42 is arranged between the housing 40 and the third filter element 30. The insulation layer may comprise an insulating polymeric foam material, which is optionally covered by EPDM (ethylene propylene diene monomer) rubber to protect the foam. The insulation layer 42 and the third filter element 30 are arranged at a distance from each other in a direction D perpendicular to the axial direction X of the device. In this way reducing agent in the form of liquid can be sucked by the pump 21 to a chamber formed in the gap between the insulation layer and the third filter element 30. Due to the force created by the pump 21, the liquid is sucked through the third filter element 30 as shown by arrows on the left hand side of the filter device 23 in Fig. 3. The third filter element is illustrated only in the left hand side, but is included in a symmetrical way over the whole circumference of the outer filter unit 29. Since the third filter element is located upstream of the pump, i.e. on the vacuum side of the pump 21, particulate matter is filtered from the reducing agent before the liquid enters the pump 21. The pump 21 pressurizes the reducing agent such that it is subsequently forced through the first filter element 26 and second filter element 28 of the inner filter unit 27, which are located on the pressurized side of the pump.

As shown in Fig. 3, an enclosure 44 is arranged to surround the inner filter unit 27 in a liquid tight manner. The enclosure 44 functions together with a cover means 50 to protect the pressurized side of the pump 21, and thus the pressurized side of the filter device 23. The enclosure 44 is made of a material which is both pressure proof and heat conducting, such as metal. To ensure that a liquid tight seal is formed, sealing means 44' and 54' are arranged between the cover means 50 and the enclosure 44. The enclosure 44 is arranged at a distance from the first filter element 26 and the third filter element 30 in a radial direction, i.e. the direction perpendicular to the axial direction X of the filter device. Further sealing elements 54' (only one of which is depicted with reference sign) are arranged in the device between the insulation layer 42 and the cover means 50 and a collar 26a of the first filter element 26. In this way, liquid tight filter device can be provided. Since the enclosure 44 is made of a material which is heat conducting, problems caused by temperature variations, such as freezing problems, may de decreased, since heat is directly conducted from the vacuum side of the device to the pressurized side of the device and vice versa. To further decrease possible problems with liquid expansion in case the liquid freezes, a foam material element 46 can be arranged inside a hollow central tube 25. The foam material element 46 may be of any polymeric foam material, and may be covered by EPDM (ethylene propylene diene monomer) rubber to protect the foam element 46.

The first filter element 26 and the second filter element 28 extend in an axial direction X of the filter device 23, and in a direction perpendicular to the axial direction, i.e. direction depicted with D, of the filter device. The second filter element 28 is arranged coaxially with the first filter element 26 and such that the first filter element 26 surrounds the second filter element 28. The second filter element 26 constitutes the hollow central tube 25 of the reducing agent filter device 23. The reducing agent filter device 23 further comprises an outer filter unit 29 comprising a third filter element 30, which at least partially surrounds the inner filter unit 27. The third filter element 30 is suitably arranged coaxially with the first filter element 26 and the second filter element 28 of the inner filter unit 27. The filter device 23 has a substantially circular cylindrical shape and the outer filter unit 29 radially surrounds the inner filter unit 27. By radially or radial direction is generally meant in this context direction D which is perpendicular to the axial direction. Also the inner and outer units are suitably essentially concentric and thus have a common central point.

Generally, the filter device may have a substantially circular cylindrical shape, i.e. the cross section of the filter device is circular. The shape of the first filter element, the second filter element and the third filter element adapt to the shape of the filter device. For example, when the shape is circular cylindrical, the cross section of the respective first, second and third filter element is spherical. However, the cross-section of the filter device may have another shape such as oval or rectangular.

The housing 40 further comprises the cover means 50, which may be re-openable. The housing 40 thus functions together with the cover means 50 to protect the vacuum side of the pump 21, and thus the vacuum side of the filter device 23. Suitably, the housing comprises at least one liquid inlet opening 51 and at least one liquid outlet opening 53. The pump 21 can be integrated with the cover means, or be located outside the cover means 50 as schematically shown in Fig. 2 and Fig. 3. The cover means 50 comprises an additional liquid inlet 51a and liquid outlet 53a to supply the liquid to and from the pump 21.

The reducing agent filter device comprises liquid pathways in which the reducing agent is arranged to flow. As illustrated by the arrows in Fig. 3, the reducing agent is first fed through the third filter element 30, secondly through the first filter element 26 and thirdly through the second filter element 28, and then further to other components of the dosing system. The dosing system may further comprise a first pressure sensor PI, which is arranged to detect the reducing agent pressure downstream of the reducing agent filter device 23. In this way, the flow pressure may be measured and checked and e.g. compared with pre-determined pressure values. The pressure sensor may be connected to a control system of the vehicle, which is provided with data regarding pre-determined pressure values. If the pressure is lower than the pre-determined values, the operator can be notified to check the filter. Optionally, the reducing agent dosing system further comprises a second pressure sensor P2 arranged to detect the reducing agent pressure upstream of the reducing agent filter device 23. In this way also the ingoing flow pressure can be measured and checked and the pressure drop over the filter device checked. In a similar manner as in connection with the first pressure sensor PI, the flow pressure drop may be measured and checked and e.g. compared with pre determined values in the control system of the vehicle. If the pressure drop is higher than the pre-determined values, the operator can be notified to check the filter. Furthermore, to improve the accuracy and to find out whether clogging is in the inner filter unit or outer filter unit a third pressure sensor P3 may be arranged downstream of the third filter element 30 and upstream of the pump 31. The pressure sensor P3 functions in a similar manner as PI and P2 and communicates with the control system of the vehicle.

As mentioned above, the third filter material may comprise a plastic or metallic net, nylon fibres or is paper-based and has a mesh size of less than or equal to 75 pm and preferably 70 pm. Thus, particulate material having a size larger than the mesh size is captured while the finer particulate material is fed further in the filter device. In this way, clogging of the third filter element is avoided while the pump 21 can be protected. The first filter material may have a finer mesh size than the second filter and can be for example a mesh size of less than or equal to 25 pm. In this way most of the impurities in form of particles can be captured by the first filter element. However, there is always a risk that a small amount, such as about 1% of the total amount of the particles, will pass the first filter element. When these particles accumulate later on in small filter devices or screens arranged in connection with components downstream of the filter device, there is a risk for clogging of the small filter devices or screens. Therefore, the second filter element 28 is arranged downstream of the first filter element 26. The second filter material may have a mesh size which is slightly coarser than the mesh size of the first filter element and can be for example a mesh size of less than or equal to 30 pm. In this way, the risk for particulate impurities clogging small filter devices in connection with components downstream of the filter device is minimized. However, the mesh size of the first and second filter elements could be the same or the mesh size of the first filter element could be coarser than the mesh size of the second filter element.

The first filter material may be of any suitable kind and may for example comprise nylon fibres and/or it may be paper-based or comprise cellulosic fibres. The second filter material may be of the same kind as the first filter material or it may be different and may comprise for example plastic and/or metallic net. Likewise, the third filter material may comprise a plastic or metallic net, nylon fibres or it can be paper-based. The foregoing description of the present invention is provided for illustrative and descriptive purposes. It is not intended to be exhaustive or to restrict the invention to the variants described. Many modifications and variations will obviously be apparent to one skilled in the art. The embodiments have been chosen and described in order best to explain the principles of the invention and its practical applications and hence make it possible for a skilled person to understand the invention for various embodiments and with the various modifications appropriate to the intended use.