SCR DEVICE WITH VALVE ARRANGEMENT

Abstract

An SCR device for a motor vehicle, comprising a tank for storing reducing liquid, an injection device for injection of the reducing liquid into an exhaust gas system of a motor vehicle, a liquid conduit for delivering reducing liquid from the tank to the injection device, a feed pump for conveying reducing liquid in the conduit, and a valve arrangement in the conduit, the valve arrangement designed to interrupt an injection flow in the conduit when the tank-side pressure is greater, than the injection device-side pressure in the conduit by less than an injection threshold value, and to allow the injection flow to pass when the tank-side pressure is greater by at least the injection threshold, the valve arrangement designed to interrupt a return flow in the conduit from the injection device to the tank when the injection device-side pressure is greater than the tank-side pressure by less than a return threshold value, and to allow the return flow to pass through when the injection device-side pressure is greater than the tank-side pressure in the conduit, by at least the return threshold value, the injection threshold value being greater than the return threshold value.

Claims

1-10. (canceled)

11. An SCR device for a motor vehicle, comprising a tank for storing an associated reducing liquid, in particular aqueous urea solution, an injection device for injection of the associated reducing liquid into an associated exhaust gas system of an associated motor vehicle, the SCR device having a liquid conduit for delivering the associated reducing liquid from the tank to the injection device, a feed pump for conveying the associated reducing liquid in the liquid conduit, and a valve arrangement in the liquid conduit, the valve arrangement being designed to interrupt an injection flow in the liquid conduit from the tank to the injection device when a tank-side pressure in the liquid conduit on a tank side of the valve arrangement is greater, in terms of amount, than an injection device-side pressure in the liquid conduit on an injection device side of the valve arrangement, by less than an injection threshold value, and to allow the injection flow to pass through when the tank-side pressure is greater, in terms of amount, than the injection device-side pressure, by at least the injection threshold value, the valve arrangement being designed to interrupt a return flow in the liquid conduit from the injection device to the tank when the injection device-side pressure is greater, in terms of amount, than the tank-side pressure in the liquid conduit, by less than a return threshold value, and to allow the return flow to pass through when the injection device-side pressure is greater, in terms of amount, than the tank-side pressure in the liquid conduit, by at least the return threshold value, the injection threshold value being greater in terms of amount than the return threshold value.

12. The SCR device according to claim 11, wherein the valve arrangement is arranged between the feed pump and the injection device.

13. The SCR device according to claim 11, further comprising a filter, wherein the valve arrangement is arranged between the filter and the feed pump.

14. The SCR device according to claim 11, wherein the feed pump is a bidirectionally operating pump that is designed to produce both the pressure difference that causes the injection flow and also the pressure difference that causes the return flow.

15. The SCR device according to claim 11, wherein the tank has a predetermined rated maximum filling level, and wherein the injection threshold value is greater than a hydrostatic pressure that is produced by reducing the associated liquid introduced up to the rated maximum filling level.

16. The SCR device according to claim 11, wherein at least one of a maximum flow rate of the injection flow does not exceed 7 l/h and the maximum flow rate of the return flow does not exceed 3.5 l/h.

17. The SCR device according to claim 11, wherein at least one of a maximum flow rate of the injection flow is between 3 and 6 l/h and the maximum flow rate of the return flow is between 0 and 3 l/h.

18. The SCR device according to claim 11, wherein the valve arrangement has at least one valve body that is biased into a closed position in opposing working directions with different strengths by at least one pretensioning device.

19. The SCR device according to claim 11, wherein the valve arrangement includes a first valve body and a second valve body, the first valve body being biased into a closed position in a first working direction by a first pretension force, and the second valve body being biased into a closed position in a second working direction by a second pretension force, the first working direction being opposite of the second working direction, the first pretension force being greater than the second pretention force.

20. The SCR device according to claim 19, wherein at least one of the first pretension force and the second pretension force is produced by a pretensioning device.

21. The SCR device according to claim 19, wherein the first valve body is an injection valve body that is in an opened position during the injection flow and the second valve body is a return valve body that is in an opened position during the return flow.

22. The SCR device according to claim 19, wherein the first valve body is an injection valve body that is in an opened position only during the injection flow and the second valve body is a return valve body that is in an opened position only during the return flow.

23. The SCR device according to claim 11, wherein the valve arrangement has a separate valve body for each of the injection flow and the return flow, and at least the injection valve body associated with the injection flow is biased into a closed position by a pretensioning device.

24. The SCR device according to claim 18, wherein the at least one valve body includes at least one of a valve ball and an umbrella valve body.

25. The SCR device according to claim 24, wherein the at least one valve body are all the same type of valve body.

26. The SCR device according to claim 11, wherein on the injection device side of the valve arrangement, the liquid conduit can be operationally separated, preferably from a valve housing of the valve arrangement.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail and illustrated in the accompanying drawings which form a part hereof and wherein:

[0028] FIG. 1 shows a rough schematic representation of an SCR device according to the invention; and,

[0029] FIG. 2 shows a cross-sectional view through an example of a valve arrangement as it could be used in the SCR device according to FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0030] Referring now to the drawings wherein the showings are for the purpose of illustrating preferred and alternative embodiments of the invention only and not for the purpose of limiting the same, FIG. 1 shows an SCR device according to certain aspects of the invention that is designated generally by 10. The SCR device, which serves for reduction of nitrogen oxides in the exhaust gas of an internal combustion engine of a motor vehicle, comprises a tank 12, in which reducing liquid 14, for example aqueous urea solution, can be introduced up to a rated filling level 16 according to regulations. A filling line and the like is not shown in FIG. 1, since it does not play any further role for the SCR device according to the present invention.

[0031] The reducing liquid 14 can be conveyed by means of a liquid conduit 18 to an injection device 20, where it is injected into an exhaust gas from an internal combustion engine in an exhaust gas system that is not shown in FIG. 1.

[0032] In order to convey the reducing liquid 14 from the tank 12 to the injection device 20 a feed pump 22 is provided, for instance in the form of a reversible geared pump.

[0033] As is indicated by the arrows pointing in the opposite direction, the feed pump 22 can produce both an injection flow E from the tank 12 to the injection device 20 and also a return flow R in the reverse direction from the injection device 20 into the tank 12. As is indicated by the smaller triangle pointing in the direction of the return flow R, the feed pump 22 conveys in the return direction with a smaller volume or mass flow than in the injection flow direction.

[0034] A filter housing 24, preferably provided directly on or in the tank 12, is provided for purification of the reducing liquid 14 conveyed to the injection device 20.

[0035] In order to ensure that reducing liquid 14 actually only flows in the liquid conduit 18 when a corresponding pressure gradient is implemented in the liquid conduit 18 by the feed pump 22, the SCR device 10 comprises a valve arrangement 26 that is preferably arranged between the feed pump 22 and the injection device 20. A valve arrangement 26′ can also be arranged, additionally or alternatively, between the tank 12 or the filter 24 and the feed pump 22.

[0036] Since the valve arrangement 26 is designed to prevent a leakage flow of reducing liquid 14 from the tank 12 to the injection device 20 if the feed pump 22 is not correspondingly in operation, between the valve arrangement 26 and the liquid conduit 18, more precisely the liquid conduit portion 18a on the injection device side 26a of the valve arrangement 26, a line connection 28 can be provided that is detachable in operation and enables a proper detachability of the liquid conduit 18 from the valve arrangement 26, for example, for repair and/or maintenance. The same applies for a reconnection of the liquid conduit 18 on the injection device side 26a of the valve arrangement 26.

[0037] The side 26b of the valve arrangement 26 that is opposite the injection device 26a, is directed towards the tank 12 and is connected thereto is the tank side 26b of the valve arrangement 26.

[0038] A possible construction of the valve arrangement 26 is shown roughly schematically in FIG. 2.

[0039] The valve arrangement 26 can have a valve housing 30, in which valve bodies 32 and 34 can be movably provided.

[0040] The two valve bodies 32 and 34 are preferably configured identically, in the illustrated example as an umbrella valve body. In this case the valve body 32 is an injection valve body 32 that interrupts an injection flow E until the pressure difference between the tank side 26b and the injection device side 26a of the valve arrangement 26 exceeds a predetermined pressure difference. With a predetermined configuration of the injection valve 32, the pressure difference, that is sufficient for a displacement of the injection valve body 32 out of the closed position shown in FIG. 2 into an open position allowing the injection flow E, is adjustable by the spring stiffness of a valve spring 36 by which the injection valve body 32 is preferably biased into the closed position shown in FIG. 2.

[0041] In the closed position the injection valve body 32 closes through openings 38 and 40 for the injection flow E through the valve arrangement 26.

[0042] The valve spring 36, that is supported on the long end of the valve stem of the injection valve body 32 facing away from the valve, is selected so that with a predetermined configuration of the injection valve body 32 this valve remains in the closed position under the action of the hydrostatic pressure of the reducing liquid 14 accommodated in the tank 12, even when the reducing liquid 14 is introduced into the tank 12 up to its rated maximum filling level 16. The valve spring 36 is preferably designed with a safety margin, that also enables the rated maximum filling level 16 in the tank 12 to be exceeded without the resulting hydrostatic pressure of the reducing liquid 14 being able to move the injection valve body 32 out of the closed position.

[0043] The valve body 34 is the return valve body 34 that is open for the return flow R and is closed for the injection flow E.

[0044] The return valve body 34 and the arrangement thereof in the valve housing 30 correspond to that of the injection valve body 32, only in the opposite direction, and therefore, taking the difference of direction into consideration, reference is made to the foregoing description of the injection valve body 32 for explanation of the return valve body 34.

[0045] The pressure difference at which the return valve body 34 is open for the return flow R is less, in terms of amount, than the pressure difference that is necessary for a displacement of the injection valve body 32 out of the closed position.

[0046] In the case of the preferred use of identical valve bodies 32 and 34, this pressure difference can be achieved by the use of a weaker valve spring or by the complete omission of a valve spring.

[0047] Since in comparison to the injection flow E the return flow R usually takes place with a lower flow rate, it is justified for the return valve body 34 to exit the closed position. Biasing into the closed position, as illustrated in FIG. 2, is not necessary, but takes place in any case due to the hydrostatic pressure of the reducing liquid 14 on the tank side 26b of the valve arrangement 26. Therefore, for the return flow R it is only necessary to overcome the friction existing between the valve housing 30 and the return valve body 34 in order to displace the return valve body 34 out of the closed position illustrated in FIG. 2 into an open position.

[0048] Thus when the injection device 20 is not in use, for example when the motor vehicle and the internal combustion engine are switched off, by means of the single feed pump 22 the liquid conduit 18 can be emptied at least in the portion extending from the feed pump 22 to the injection device 20, so that the conduit portion 18a of the liquid conduit 18 located between the valve arrangement 26 and the injection device 20 can be released without undesirable escape of reducing liquid from the valve arrangement 26. For this purpose, the valve arrangement 26, in particular the valve housing 30, can have a thread as a releasable connecting device 28 for connection of the valve arrangement 26 to the liquid conduit 18. The internal thread can be provided on both sides of the valve arrangement 26, in order to remove the valve arrangement 26, if necessary, completely from the liquid conduit 18. The thread formation on the tank side 26b of the valve housing 30 is designated by 42. to be able Thus connection pieces of the liquid conduit can be screwed into the internal thread 28 and 42 in order to achieve a liquid-tight connection.

[0049] While considerable emphasis has been placed on the preferred embodiments of the invention illustrated and described herein, it will be appreciated that other embodiments, and equivalences thereof, can be made and that many changes can be made in the preferred embodiments without departing from the principles of the invention. Furthermore, the embodiments described above can be combined to form yet other embodiments of the invention of this application. Accordingly, it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.