GB2593220A

GB2593220A - An air-assisted liquid selective catalytic reduction metering system

Info

Publication number: GB2593220A
Application number: GB2004088.7A
Authority: GB
Inventors: Rose Fleur
Original assignee: Delphi Technologies IP Ltd
Current assignee: Delphi Technologies IP Ltd
Priority date: 2020-03-20
Filing date: 2020-03-20
Publication date: 2021-09-22
Also published as: GB202004088D0

Abstract

An air assisted metering system for a selective catalytic reduction system including a positive displacement pump 13 comprising a chamber 21 for pressurising a diesel exhaust fluid (DEF) drawn from a DEF tank 12, and a chamber 22 for containing air received from an air source, wherein the DEF chamber 21 has a first intake line 14 connected to the DEF tank, and a first output line 15 connected to a spray nozzle 15, and the air chamber 22 has a second intake line 17 connected to an air source, and a second output line connected to the spray nozzle, such that the DEF and air mix at said nozzle. This reduces the space and weight required for the metering system. The positive displacement may comprise for example a diaphragm, piston or plunger pump. The pump may be arranged to pressurise the air in the air chamber for example when driven by a solenoid 27. The pump may be alternately driven by a supply of compressed air provided to the air chamber.

Description

AN AIR-ASSISTED LIQUID SELECTIVE CATALYTIC REDUCTION

METERING SYSTEM

TECHNICAL FIELD

The present disclosure relates to a metering system for use in an air-assisted liquid selective catalytic reduction (SCR) system.

BACKGROUND

SCR systems are used to reduce nitrogen oxide (N0x) emissions from diesel fuelled internal combustion engines. In such systems, a metered dose of diesel exhaust fluid (DEF) is injected into the engine exhaust system. When subjected to high temperatures, DEF decomposes into ammonia which chemically reacts with metallic elements in the SCR system to produce nitrogen and water.

The DEF typically comprises an aqueous urea solution such as AdBlue (RTM) which is injected into the engine exhaust system as a fine spray or mist.

An example prior art SCR system 1 is illustrated in Figure 1. The SCR system 1 comprises a tank 2 for storing a supply of DEF. The tank 2 is in fluidic communication with the inlet of a piston pump 3 via a DEF inlet line 4. The outlet of the piston pump 3 is in fluidic communication with an inlet of a spray nozzle 5 by a DEF output line 6.

Although not shown, the DEF output line 6 may comprise an accumulator located in the DEF output line 6 between the piston pump 3 and the spray nozzle 5. As is well known in the art, the provision of an accumulator in the DEF output line 6 smooths pressure variations, caused by the intermittent nature of the piston pump output, in the DEF supplied to the spray nozzle 5.

The spray nozzle 5 is additionally in fluidic communication with a supply 7 of compressed air which passes through the spray nozzle 5 together with the pressurised DEF to create a fine spray for injection into the engine exhaust system. The supply 7 of compressed air may either comprise a compressed air tank or an air compressor provided as part of the SCR system. A control unit 8 controls the operation of the piston pump 3 and the supply 7 of compressed air in use.

The system described hereinbelow provides improvements over known SCR systems.

SUMMARY OF THE INVENTION

The present invention provides an air-assisted liquid selective catalytic reduction metering system comprising: a positive displacement pump for pressurising a supply of diesel exhaust fluid; a tank for storing a supply of diesel exhaust fluid; and a nozzle for atomising the diesel exhaust fluid, characterised in that the positive displacement pump comprises: a diesel exhaust fluid chamber in fluidic communication with the storage tank via a diesel exhaust fluid intake line, and in fluidic communication with the nozzle via a diesel exhaust fluid output line; and an air chamber in fluidic communication with an air supply via an air intake line, and in fluidic communication with the nozzle via an air output line.

The use of a positive displacement pump capable of supplying both pressurised DEF and compressed air to the nozzle is advantageous as less hardware, packaging space and weight is required for the metering system in comparison to

prior art systems.

Optionally, the positive displacement pump may be a compressed air activated positive displacement pump. This is particularly beneficial if there is a source of compressed air located on the vehicle.

Alternatively, the positive displacement pump may be configured to compress the supply of air in the air chamber in use. This is beneficial over existing systems in which air is compressed by the SCR system since only one pump is required to compress both the DEF and the air.

The positive displacement pump may optionally be a solenoid activated positive displacement pump. Solenoid activated piston pumps are particularly advantageous as they provide accurate metering control.

Optionally the positive displacement pump comprises a piston pump, a plunger pump, or a diaphragm pump depending on the specific design.

Optionally the active volume of the diesel exhaust fluid chamber is not equal to the active volume of the air chamber so that different compression requirements and packaging requirements may be met.

The positive displacement pump is optionally configured so that, in use, the diesel exhaust fluid chamber is evacuated via the diesel exhaust fluid output line as air enters the air chamber via the air intake line. In this way, the DEF may be compressed as the air chamber fills and the air may be compressed, or may move through the positive displacement pump, as the DEF chamber fills.

The positive displacement pump may be configured so that, in use, the direction of fluid flow on entry to and exit from at least one of the diesel exhaust fluid chamber or air chamber is substantially parallel to the displacement direction of the positive displacement pump. Such a configuration allows efficient in-line packaging of the SCR metering system.

The positive displacement pump may be configured so that, in use, the direction of fluid flow on entry to and exit from at least one of the diesel exhaust fluid chamber or air chamber is substantially perpendicular to the displacement direction of the positive displacement pump to provide alternative packaging options.

Optionally the diesel exhaust fluid output line comprises an accumulator for dampening pressure fluctuations in the pressurised diesel exhaust fluid.

Non-return valves may optionally be located substantially at the interface between the positive displacement pump and the diesel exhaust fluid intake and output lines and the air intake and output lines to prevent back flow through the pump.

In another aspect, the present invention provides a vehicle comprising an air-assisted liquid selective catalytic reduction metering system as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of non-limiting examples with reference to the following figures, in which: Figure 1 shows a schematic illustration of a prior art SCR system; Figure 2 shows a schematic illustration of an improved SCR system in accordance with the invention; Figure 3 shows a schematic illustration of an alternative pump configuration for use in the SCR system of the invention; Figure 4 shows a schematic illustration of another pump configuration for use in the SCR system of the invention; Figure 5 shows a schematic illustration of yet another pump configuration for use in the SCR system of the invention; Figure 6 shows a schematic illustration of a still further pump configuration for use in the SCR system of the invention; and Figure 7 shows a schematic illustration of the SCR system of the invention installed in a vehicle.

DETAILED DESCRIPTION

An example prior art SCR system 1 is shown in Figure 1 and described above. Figure 2 shows an improved SCR system 10. The SCR system 10 comprises a tank 12 for storing a supply of DEF, a dual chamber positive displacement pump 13, and a spray nozzle 15. A control unit 9 controls the operation of the SCR system 10.

The dual chamber positive displacement pump 13 comprises an outer housing 20 which surrounds two chambers 21, 22 located within the housing 20. A first of the chambers 21 is connected to the tank 12 via a DEF inlet line 14, and connected to the spray nozzle 15 via a DEF output line 16. The first chamber 21 is therefore configured to pump DEF from the tank 12 to the spray nozzle 15 in use and is referred to herein as DEF chamber 21. Both the DEF inlet line 14 and the DEF output line 16 have non-return valves 11 located at the entry/exit of the DEF chamber 21 to prevent backflow during use.

The second chamber 22 is connected to an air supply (not shown) via an air inlet line 17 and connected to the spray nozzle 15 via an air output line 18. The second chamber 22 is therefore configured to provide compressed air to the spray nozzle 15 in use and is referred to herein as air chamber 22. Both the air inlet line 17 and the air output line 18 have non-return valves 11 located at the entry/exit of the air chamber 22 to prevent backflow during use.

The DEF chamber 21 and the air chamber 22 are separated by a rigid wall 23 through which a piston shaft 24 passes. The piston shaft 24 comprises a DEF side piston 25 located at one end of the piston shaft 24 and an air side piston 26 located at the other end of the piston shaft 24. Seals (not shown) are provided between the DEF side piston 25 and the housing 20 and the air side piston 26 and the housing 20. A seal may also be provided between the piston shaft 24 and the rigid wall 23 The piston shaft 24, and hence the pistons 25, 26, are activated by a solenoid 27 which surrounds the housing 20.

In this example embodiment, the DEF output line 16 comprises an accumulator 19 located in the DEF output line 16 between the pump 13 and the spray nozzle 15. The accumulator 19 smooths pressure variations in the DEF supplied to the spray nozzle 15 caused by the intermittent nature of the action of the positive displacement pump 13. In an alternative embodiment (not shown) no accumulator 19 is present.

The air supply to air inlet line 17 may comprise air at substantially atmospheric pressure, for example as supplied via an air intake located on the body of a vehicle. Alternatively, the air supply to the air intake line 17 may comprise compressed air received from another air compressor located on the vehicle. In the case where air at substantially atmospheric pressure is supplied to the air intake line 17, all of the required air compression is achieved by piston 26 on the air chamber 22 side of the positive displacement pump 13.

In the case where compressed air is supplied to the air intake line 17, the piston 26 on the air chamber 22 side of the positive displacement pump 13 may be used to increase to pressure of the supplied air. Alternatively, the positive displacement pump 13 may be driven by the compressed air supply such that the solenoid 27 can be dispensed with. A compressed air operated pump 13 has the advantage that less packaging space and weight is required in the SCR system 10.

Figure 3 shows an alternative dual chamber positive displacement pump 40 suitable for use in the SCR system 10. Like reference numerals are used throughout to indicate like components for simplicity.

The pump 40 comprises an outer housing 30 which surrounds two chambers 31, 32 located within the housing 30. A first chamber comprises a DEF chamber 31 which is connected to the tank 12 via the DEF inlet line 14, and connected to the spray nozzle 15 via the DEF output line 16. The second chamber comprises an air chamber 32 which is connected to an air supply (not shown) via the air inlet line 17, and connected to the spray nozzle 15 via the air output line 18. As before, all inlets/outlets from the chambers 31, 32 have non-return valves 11 to prevent backflow from the chambers 31, 32 in use.

The DEF chamber 31 and the air chamber 32 are separated by a rigid wall 33 through which a piston shaft 34 passes. The piston shaft 34 comprises a DEF side piston 35 located at one end of the piston shaft 34, and an air side piston 36 located at the other end of the piston shaft 34. Seals (not shown) are provided between the DEF side piston 35 and the housing 30 and the air side piston 36 and the housing 30. A seal may also be provided between the piston shaft 34 and the rigid wall 33. The piston shaft 34, and thereby the pistons 35, 36, are activated by a solenoid 37 which surrounds the housing 30.

In the example embodiment of Figure 3, the DEF chamber 31 has a larger capacity than the air chamber 32 and the piston 35 has a larger surface area than the piston 36. It is therefore possible to tune the amount of compression produced by the pump 40 in each of its two chambers 31, 32 depending on the particular requirements of the SCR system 10 or spray nozzle 15 for example. It is not necessary that that DEF chamber 31 be larger than the air chamber 32, and an opposite arrangement of a larger air chamber 32 than DEF chamber 31 may be used if desired.

As above for the pump 13 of Figure 2, the air supply to the air inlet line 17 may be air at substantially atmospheric pressure or may be compressed air from another source on the vehicle. Once again, if compressed air is used as the air supply source, the pump 40 may be driven by the compressed air and the solenoid 37 may be dispensed with.

The DEF inlet 14 and output 16 lines, and the air inlet 17 and output 18 lines enter and exit the DEF 31 and air 32 chambers respectively in a direction which substantially parallel to the displacement direction of the positive displacement pump 40 so that on entry to and exit from the chambers 31, 32 direction of fluid flow of the DEF or air is substantially parallel to the displacement direction of the pump 40 which corresponds to the major axis of the piston shaft 34. Alternatively, the DEF inlet 14 and output 16 lines, and the air inlet 17 and output 18 lines may enter/exit the chambers 31, 32 in a direction which is substantially perpendicular to the displacement direction of the positive displacement pump 40, or at any angle best suited to the requirements of the system. It is not necessary that the inlet/output line orientations with respect to both chambers 31, 32 is the same such that one chamber may have substantially parallel inlet/output lines, and the other may have substantially perpendicular inlet/output lines, or any other suitable orientation.

Figure 4 shows another dual chamber positive displacement pump 60 suitable for use in the SCR system 10. In this example embodiment, the dual chamber positive displacement pump 60 comprises a dual chamber plunger pump.

The pump 60 comprises an outer housing 50 which surrounds two chambers 51, 52 located within the housing 50. A first chamber comprises a DEF chamber 51 which is connected to the tank 12 via the DEF inlet line 14, and connected to the spray nozzle 15 via the DEF output line 16. The second chamber comprises an air chamber 52 which is connected to an air supply (not shown) via the air inlet line 17 and connected to the spray nozzle 15 via the air output line 18. As above, all inlets/outlets from the chambers 51, 52 have non-return valves 11 to prevent backflow from the chambers 51, 52 in use.

The DEF chamber 51 and the air chamber 52 are separated by a rigid wall 53. A first plunger 55 passes through the housing 50 into the DEF chamber 51 and a second plunger 56 passes through the housing 50 into the air chamber 52. The first and second plungers 55, 56 are rigidly connected to form a plunger assembly 54 such that the two plungers 55, 56 move in unison. Seals (not shown) are provided between the DEF side plunger 55 and the housing 50 and the air side plunger 56 and the housing 50. The plunger assembly 54 is activated by a solenoid 57 which surrounds the plunger assembly 54.

If needed, the DEF chamber 51 may have a larger or smaller capacity than the air chamber 52, and the plunger 55 may have a larger or smaller surface area than the plunger 56 in order to achieve the required amounts of compression and/or flow in the SCR system 10.

As above, the air supply to the air inlet line 17 may be air at substantially atmospheric pressure or may be compressed air from another source on the vehicle. Once again, if compressed air is used as the air supply source, the pump 60 may be driven by the compressed air and the solenoid 57 may be dispensed with.

Figure 5 shows another alternative dual chamber positive displacement pump 80 suitable for use in the SCR system 10. In this example embodiment, the dual chamber positive displacement pump 80 comprises a dual chamber diaphragm pump.

The pump 80 comprises an outer housing 70 which surrounds two chambers 71, 72 located within the housing 70. A first chamber comprises a DEF chamber 71 which is connected to the tank 12 via the DEF inlet line 14, and connected to the spray nozzle 15 via the DEF output line 16. The second chamber comprises an air chamber 72 which is connected to an air supply (not shown) via the air inlet line 17 and connected to the spray nozzle 15 via the air output line 18. Once again, all inlets/outlets from the chambers 71, 72 have non-return valves 11 to prevent backflow from the chambers 71, 72 in use.

The DEF chamber 71 and the air chamber 72 are separated by a rigid wall 73. A first diaphragm 75 is located in the DEF chamber 71 and a second diaphragm 76 is located in the air chamber 72. The diaphragms 75, 76 are activated by a solenoid 77 which surrounds the housing 70. Alternatively the solenoid 77 may be located within the housing 70.

If needed, the DEF chamber 71 may have a larger or smaller capacity than the air chamber 72, and the diaphragm 75 may have a larger or smaller surface area or displacement capacity than the diaphragm 76 in order to achieve the required amounts of compression and/or flow in the SCR system 10.

In this example embodiment, the air supply to the air inlet line 17 may be air at substantially atmospheric pressure or may be compressed air from another source on the vehicle. However, in contrast to the example embodiments described above, compressed air cannot be used to activate both sides the pump 80.

Unlike in the other example embodiments discussed above, the pump 80 may be configured to operate substantially synchronously so that both the DEF chamber 71 and the air chamber 72 fill and discharge at the same time. Alternatively the synchronisation of the chamber fill/discharge cycles may be configured to be out of phase by any desired amount.

This is in contrast to the pumps 13, 40, 60 of the above example embodiments which, due to the rigid link between their pistons/plungers, can only be operated 180° out of phase.

In a further alternative example shown in Figure 6, the first 75 and second 76 diaphragms 75, 76, and the rigid dividing wall 73, may be replaced by a single diaphragm 78 which may either be driven by a solenoid 77 or by a source of compressed air.

It will be understood that the above described embodiments are examples only and that other configurations are possible. In particular, it will be understood that an accumulator 19 may be located in the DEF output line 16 of any of the above described embodiments. In addition, although the example embodiments described above have the same type of displacement pump mechanism on each side of the dual chamber displacement pumps 13, 40, 60, 80, it is envisioned that different displacement pump mechanisms may be used on either side of the dual chamber displacement pump. For example, the dual chamber displacement pump may comprise a piston pump mechanism on one side and a plunger or diaphragm pump mechanism on the other side. Any suitable combination of displacement pump mechanisms may be used. In addition, the SCR system 10 may comprise more than on nozzle such that the dual chamber displacement pumps 13, 40, 60, 80 may be used to supply DEF and air to more than one nozzle concurrently.

Claims

CLAIMS: 1. An air-assisted liquid selective catalytic reduction metering system 10 comprising: a positive displacement pump 13 for pressurising a supply of diesel exhaust fluid; a tank 12 for storing a supply of diesel exhaust fluid; and a nozzle 15 for atomising the diesel exhaust fluid, characterised in that the positive displacement pump 13 comprises: a diesel exhaust fluid chamber 21 in fluidic communication with the storage tank 12 via a diesel exhaust fluid intake line 14, and in fluidic communication with the nozzle 15 via a diesel exhaust fluid output line 16, wherein the positive displacement pump 13 is configured to compress the supply of diesel exhaust fluid in the diesel exhaust chamber 21 in use; and an air chamber 22 in fluidic communication with an air supply via an air intake line 17, and in fluidic communication with the nozzle 15 via an air output line 18.
2. An air-assisted liquid selective catalytic reduction metering system 10 as claimed in claim 1, wherein the positive displacement pump 13 is a compressed air activated positive displacement pump.
3. An air-assisted liquid selective catalytic reduction metering system 10 as claimed in claim 1, wherein the positive displacement pump 13 is configured to compress the supply of air in the air chamber 22 in use.
4. An air-assisted liquid selective catalytic reduction metering system 10 as claimed in claim 1 or claim 3, wherein the positive displacement pump 13 is a solenoid activated positive displacement pump.
5. An air-assisted liquid selective catalytic reduction metering system 10 as claimed in any preceding claim, wherein the positive displacement pump 13, 40, 60, 80 comprises a piston pump, a plunger pump, or a diaphragm pump.
6. An air-assisted liquid selective catalytic reduction metering system 10 as claimed in any preceding claim, wherein the active volume of the diesel exhaust fluid chamber 31 is not equal to the active volume of the air chamber 32.
7. An air-assisted liquid selective catalytic reduction metering system 10 as claimed in any preceding claim, wherein the positive displacement pump 13 is configured so that, in use, the diesel exhaust fluid chamber 21 is evacuated via the diesel exhaust fluid output line 16 as air enters the air chamber 22 via the air intake line 17.
8. An air-assisted liquid selective catalytic reduction metering system 10 as claimed in any preceding claim, wherein the positive displacement pump 40 is configured so that, in use, the direction of fluid flow on entry to and exit from at least one of the diesel exhaust fluid chamber 31 or air chamber 32 is substantially parallel to the displacement direction of the positive displacement pump 40.
9. An air-assisted liquid selective catalytic reduction metering system 10 as claimed in any preceding claim, wherein the positive displacement pump 13 is configured so that, in use, the direction of fluid flow on entry to and exit from at least one of the diesel exhaust fluid chamber 31 or air chamber 32 is substantially perpendicular to the displacement direction of the positive displacement pump 13.
10. An air-assisted liquid selective catalytic reduction metering system 10 as claimed in any preceding claim, wherein the diesel exhaust fluid output line 16 comprises an accumulator 19 for dampening pressure fluctuations in the pressurised diesel exhaust fluid.
11. An air-assisted liquid selective catalytic reduction metering system 10 as claimed in any preceding claim, comprising non-return valves 11 located substantially at the interface between the positive displacement pump 13 and the diesel exhaust fluid intake 14 and output 16 lines and the air intake 17 and output 18 lines.
12. A vehicle 90 comprising an air-assisted liquid selective catalytic reduction metering system 10 as claimed in any preceding claim.