Selective catalytic reduction system

Abstract

A selective catalytic reduction system 20 for an internal combustion engine comprising a storage tank 22, a pump assembly 30 configured to pressurise a reducing agent from the tank and a dosing module

Description

Field of the Invention This invention relates to a selective catalytic reduction system for an internal combustion engine, in particular for a diesel internal combustion engine. Background to the Invention Selective catalytic reduction (SCR) systems are typically installed in vehicles with internal combustion engines to convert nitrogen oxides from exhaust gases to water and nitrogen gas. SCR systems may inject or spray a liquid reducing agent upstream of a catalyst of a vehicle exhaust system of the internal combustion engine to facilitate the conversion. SCR systems are typically made up of a tank, a pump module or pump, and a dosing module or doser. When the vehicle is in use, the SCR system is activated and the pump extracts the reducing agent from the tank for delivery to the doser which is operated to inject or spray the reducing agent into the exhaust system of the internal combustion engine. An SCR system may be required to function under relatively harsh temperatures which can be detrimental to the condition and lifespan of the SCR system. Reducing agents, such as ammonia or urea solution, typically have low freezing temperatures and may freeze within the components and / or passages of the SCR system if exposed to a low temperature atmosphere. The freezing of the reducing agent can result in its expansion which can cause damage to the SCR system. It is therefore common practice to purge, flush, or aerate the SCR system to ensure any residual reducing agent is not present in the SCR system when reducing agent is not being delivered into the exhaust system. It is important for SCR systems to be cost effective and have a compact packaging size to comply with vehicle characteristics and requirements while being effective at preventing reducing agent from freezing within the SCR system. It is against this background that the invention has been devised. Summary of the Invention According to an aspect of the invention, there is provided a selective catalytic reduction system for an internal combustion engine. The selective catalytic reduction system comprises: a storage tank configured to store a reducing agent; a pump assembly comprising an inlet and an outlet, the pump assembly being configured to pressurise the reducing agent; a dosing module configured to deliver the reducing agent to an exhaust system of the internal combustion engine; and a valve arrangement for providing a connection between the storage tank, the pump assembly, and the dosing module. In a first operation mode, the valve arrangement connects the inlet of the pump assembly to the storage tank and connects the outlet of the pump assembly to the dosing module. In a second operation mode, the valve arrangement connects the inlet of the pump assembly to the dosing module and connects the outlet of the pump assembly to the storage tank. Advantageously, the selective catalytic reduction system uses a single pump assembly to deliver reducing agent into a vehicle exhaust in the first operation mode and aerate the system to purge any reducing agent in the components and / or passages of the system in the second operation mode. The number of pump components required to operate the SCR system can therefore be reduced, increasing the compactness and cost effectiveness of the selective catalytic reduction system. In an embodiment, the valve arrangement may comprise at least one directional valve operable to switch between a first position corresponding to the first operation mode and a second position corresponding to the second operation mode. In an embodiment, the at least one directional valve may be operable to a non-energized state when in the first operation mode and may be operable to an energized state when in the second operation mode. Alternatively, the at least one directional valve may be operable to an energized state when in the first operation mode and may be operable to a non-energized state when in the second operation mode. In an embodiment, the valve arrangement may comprise a first directional valve connected to a first fluid line between the storage tank and the pump assembly, the first directional valve being operable to switch between a first position of the first directional valve and a second position of the first directional valve. For example, a first check valve may be disposed in the first fluid line. In an embodiment, the first directional valve may comprise: a first fluid line configuration of the first directional valve for connecting to a first plurality of fluid lines while in the first position of the first directional valve; and a second fluid line configuration of the first directional valve for connecting to the first plurality of fluid lines while in the second position of the first directional valve. In an embodiment, the valve arrangement may comprise a second directional valve connected to a second fluid line between the pump assembly and the dosing module, the second directional valve being operable to switch between a first position of the second directional valve and a second position of the second directional valve. In an embodiment, the second directional valve may comprise: a first fluid line configuration of the second directional valve for connecting to a second plurality of fluid lines while in the first position of the second directional valve; and a second fluid line configuration of the second directional valve for connecting to the second plurality of fluid lines while in the second position of the second directional valve. For example, the first and second directional valves may be operable together to switch between the first operation mode and the second operation mode. In an embodiment, the valve arrangement may comprise a third directional valve connected to a third fluid line between the pump assembly and the storage tank, the third directional valve being operable to switch between a first position of the third directional valve and a second position of the third directional valve. In an embodiment, the third directional valve may connect to a third plurality of fluid lines. The third directional valve may block a connection to the third plurality of fluid lines while in the first position of the third directional valve, and open the connection to the third plurality of fluid lines while in the second position of the third directional valve. In an embodiment, the third directional valve may be operable together with the first and second directional valves to switch between the first operation mode and the second operation mode. In an embodiment, the first directional valve may comprise: a first fluid line configuration of the first directional valve for providing a first connection to a first plurality of fluid lines while in the first position of the first directional valve; and a second fluid line configuration of the first directional valve for providing a second connection to the first plurality of fluid lines while in the second position of the first directional valve. In an embodiment, the first directional valve may be configured to control flow through the first fluid line and through the second fluid line. In an embodiment, the second check valve may be configured to control flow through the second and third fluid lines. In an embodiment, the dosing module is temporarily open during the second operation mode. In an embodiment, the valve arrangement may comprise a 3x2 directional valve and a 4x2 directional valve. The 3x2 directional valve may be capable of connecting to three fluid lines and may comprise two fluid line configurations. The 4x2 directional valve may be capable of connecting to four fluid lines and may comprise two fluid line configurations. In an embodiment, the valve arrangement may comprise a first 3x2 directional valve, a second 3x2 directional valve, and a 2x1 directional valve. Each 3x2 directional valve may be capable of connecting to three fluid lines and may comprise two fluid line configurations. The 2x1 directional valve may be capable of connecting to two fluid lines and may comprise one fluid line configuration. In an embodiment, the valve arrangement may comprise a first 3x2 directional valve and a second 3x2 directional valve. Each 3x2 directional valve may be capable of connecting to three fluid lines and may comprise two fluid line configurations. In an embodiment, the valve arrangement may comprise a 4x2 directional valve. The 4x2 directional valve may be capable of connecting to four fluid lines and may comprise two fluid line configurations. According to another aspect of the invention, there is provided a selective catalytic reduction system for an internal combustion engine. The selective catalytic reduction system comprises: a storage tank configured to store a reducing agent; a pump assembly configured to pressurise the reducing agent, the pump assembly comprising an inlet and an outlet; a dosing module configured to deliver the reducing agent to an exhaust system of the internal combustion engine; and a valve arrangement configured to provide a connection between the storage tank, the pump assembly, and the dosing module. The valve arrangement comprises a 3x2 directional valve and a 4x2 directional valve which are operable together or at substantially the same time. The 3x2 directional valve may be capable of connecting to three fluid lines and may comprise two fluid line configurations. The 4x2 directional valve may be capable of connecting to four fluid lines and may comprise two fluid line configurations. In a first operation mode, the valve arrangement connects the inlet of the pump assembly to the storage tank and connects the outlet of the pump assembly to the dosing module. In a second operation mode, the valve arrangement connects the inlet of the pump assembly to the dosing module and connects the outlet of the pump assembly to the storage tank. In an embodiment, each of the 3x2 directional valve and the 4x2 directional valve may be operable to switch between a first position corresponding to the first operation mode and a second position corresponding to the second operation mode. In an embodiment, each of the 3x2 directional valve and the 4x2 directional valve may be in a non-energized state when in the first operation mode and may be in an energized state when in the second operation mode. Alternatively, each of the 3x2 directional valve and the 4x2 directional valve may be in an energized state when in the first operation mode and may be in a non-energized state when in the second operation mode. In an embodiment, the 3x2 directional valve may be connected to a first fluid line between the storage tank and the pump assembly, the 3x2 directional valve being operable to switch between a first position of the 3x2 directional valve and a second position of the 3x2 directional valve. In an embodiment, the 3x2 directional valve may comprise: a first fluid line configuration of the 3x2 directional valve for connecting to a first plurality of fluid lines while in the first position of the 3x2 directional valve; and a second fluid line configuration of the 3x2 directional valve for connecting to the first plurality of fluid lines while in the second position of the 3x2 directional valve. In an embodiment, the 4x2 directional valve may be connected to a second fluid line between the pump assembly and the dosing module, the 4x2 directional valve being operable to switch between a first position of the 4x2 directional valve and a second position of the 4x2 directional valve. In an embodiment, the 4x2 directional valve may comprise: a first fluid line configuration of the 4x2 directional valve for connecting to a second plurality of fluid lines while in the first position of the 4x2 directional valve; and a second fluid line configuration of the 4x2 directional valve for connecting to the second plurality of fluid lines while in the second position of the 4x2 directional valve. For example, the 3x2 and 4x2 directional valves may be operable together or at substantially the same time to switch between the first operation mode and the second operation mode. According to another aspect of the invention, there is provided a selective catalytic reduction system for an internal combustion engine. The selective catalytic reduction system comprises: a storage tank configured to store a reducing agent; a pump assembly configured to pressurise the reducing agent, the pump assembly comprising an inlet and an outlet for pressurising the reducing agent; a dosing module for delivering the reducing agent to an exhaust system of the internal combustion engine; and a valve arrangement configured to provide a connection between the storage tank, the pump assembly, and the dosing module. The valve arrangement comprises a first 3x2 directional valve, a second 3x2 directional valve, and a 2x1 directional valve. Each of the first and second 3x2 directional valves may be capable of connecting to three fluid lines and may comprise two fluid line configurations. The 2x1 directional valve may be capable of connecting to two fluid lines and may comprise one fluid line configuration. The first and second 3x2 directional valves may be operable together or at substantially the same time. In a first operation mode, the valve arrangement connects the inlet of the pump assembly to the storage tank and connects the outlet of the pump assembly to the dosing module. In a second operation mode, the valve arrangement connects the inlet of the pump assembly to the dosing module and connects the outlet of the pump assembly to the storage tank. In an embodiment, each of the first and second 3x2 directional valves and the 2x1 directional valve may be operable to switch between a first position corresponding to the first operation mode and a second position corresponding to the second operation mode. In an embodiment, each of the first and second 3x2 directional valves and the 2x1 directional valve may be in a non-energized state when in the first operation mode and may be in an energized state when in the second operation mode. Alternatively, each of the first and second 3x2 directional valves and the 2x1 directional valve may be in an energized state when in the first operation mode and may be in a non-energized state when in the second operation mode. In an embodiment, the first 3x2 directional valve may be connected to a first fluid line between the storage tank and the pump assembly, the first 3x2 directional valve being operable to switch between a first position of the first 3x2 directional valve and a second position of the first 3x2 directional valve. In an embodiment, the first 3x2 directional valve may comprise: a first fluid line configuration of the first 3x2 directional valve for connecting to a first plurality of fluid lines while in the first position of the first 3x2 directional valve; and a second fluid line configuration of the first 3x2 directional valve for connecting to the first plurality of fluid lines while in the second position of the first 3x2 directional valve. In an embodiment, the second 3x2 directional valve may be connected to a second fluid line between the pump assembly and the dosing module, the second 3x2 directional valve being operable to switch between a first position of the second 3x2 directional valve and a second position of the second 3x2 directional valve. In an embodiment, the second 3x2 directional valve may comprise: a first fluid line configuration of the second 3x2 directional valve for connecting to a second plurality of fluid lines while in the first position of the second 3x2 directional valve; and a second fluid line configuration of the second 3x2 directional valve for connecting to the second plurality of fluid lines while in the second position of the second 3x2 directional valve. In an embodiment, the 2x1 directional valve may be connected to a third fluid line between the pump assembly and the storage tank, the 2x1 directional valve being operable to switch between a first position of the 2x1 directional valve and a second position of the 2x1 directional valve. In an embodiment, the 2x1 directional valve may connect to a third plurality of fluid lines. The 2x1 directional valve may block a connection to the third plurality of fluid lines while in the first position of the 2x1 directional valve, and open the connection to the third plurality of fluid lines while in the second position of the 2x1 directional valve. For example, the first and second 3x2 directional valves and the 2x1 directional valve may be operable together to switch between the firstoperation mode and the second operation mode. In an embodiment, the second check valve may be configured to control flow through the second and third fluid lines. According to another aspect of the invention, there is provided a selective catalytic reduction system for an internal combustion engine. The selective catalytic reduction system comprises: a storage tank configured to store a reducing agent; a pump assembly configured to pressurise the reducing agent, the pump assembly comprising an inlet and an outlet; a dosing module configured to deliver the reducing agent to an exhaust system of the internal combustion engine; and a valve arrangement configured to provide a connection between the storage tank, the pump assembly, and the dosing module. The valve arrangement comprises a first 3x2 directional valve and a second 3x2 directional valve. Each of the 3x2 directional valves may be capable of connecting to three fluid lines and may comprise two fluid line configurations and the first and second 3x2 directional valves may be operable together or at substantially the same time. In a first operation mode, the valve arrangement connects the inlet of the pump assembly to the storage tank and connects the outlet of the pump assembly to the dosing module. In a second operation mode, the valve arrangement connects the inlet of the pump assembly to the dosing module and connects the outlet of the pump assembly to the storage tank. In an embodiment, each of the first and second 3x2 directional valves may be operable to switch between a first position corresponding to the first operation mode and a second position corresponding to the second operation mode. In an embodiment, each of the first and second 3x2 directional valves may be in a nonenergized state when in the first operation mode and may be in an energized state when in the second operation mode. Alternatively, each of the first and second 3x2 directional valves may be in an energized state when in the first operation mode and may be in a non-energized state when in the second operation mode. In an embodiment, the first 3x2 directional valve may be connected to a first fluid line between the storage tank and the pump assembly, the first 3x2 directional valve being operable to switch between a first position of the first 3x2 directional valve and a second position of the first 3x2 directional valve. In an embodiment, the first 3x2 directional valve may comprise: a first fluid line configuration of the first 3x2 directional valve for connecting to a first plurality of fluid lines while in the first position of the first 3x2 directional valve; and a second fluid line configuration of the first 3x2 directional valve for connecting to the first plurality of fluid lines while in the second position of the first 3x2 directional valve. In an embodiment, the second 3x2 directional valve may be connected to a second fluid line between the pump assembly and the dosing module, the second 3x2 directional valve being operable to switch between a first position of the second 3x2 directional valve and a second position of the second 3x2 directional valve. In an embodiment, the second 3x2 directional valve may comprise: a first fluid line configuration of the second 3x2 directional valve for connecting to a second plurality of fluid lines while in the first position of the second 3x2 directional valve; and a second fluid line configuration of the second 3x2 directional valve for connecting to the second plurality of fluid lines while in the second position of the second 3x2 directional valve. For example, the first and second 3x2 directional valves may be operable together to switch between the first operation mode and the second operation mode. According to another aspect of the invention, there is provided a selective catalytic reduction system for an internal combustion engine. The selective catalytic reduction system comprises: a storage tank configured to store a reducing agent; a pump assembly configured to pressurise the reducing agent, the pump assembly comprising an inlet and an outlet; a dosing module configured to deliver the reducing agent to an exhaust system of the internal combustion engine; and a valve arrangement configured to provide a connection between the storage tank, the pump assembly, and the dosing module. The valve arrangement comprises a 4x2 directional valve. The 4x2 directional valve may be capable of connecting to four fluid lines and may comprise two fluid line configurations. In a first operation mode, the valve arrangement connects the inlet of the pump assembly to the storage tank and connects the outlet of the pump assembly to the dosing module. In a second operation mode, the valve arrangement connects the inlet of the pump assembly to the dosing module and connects the outlet of the pump assembly to the storage tank. In an embodiment, the 4x2 directional valve may be operable to switch between a first position corresponding to the first operation mode and a second position corresponding to the second operation mode. In an embodiment, the 4x2 directional valve may be in a non-energized state when in the first operation mode and may be in an energized state when in the second operation mode. Alternatively, the 4x2 directional valve may be in an energized state when in the first operation mode and may be in a non-energized state when in the second operation mode. In an embodiment, the 4x2 directional valve may be connected to a first fluid line between the storage tank and the pump assembly and a second fluid line between the pump assembly and the dosing module, the 4x2 directional valve being operable to switch between a first position of the 4x2 directional valve and a second position of the 4x2 directional valve. In an embodiment, the 4x2 directional valve may comprise: a first fluid line configuration of the 4x2 directional valve for providing a first connection to a first plurality of fluid lines while in the first position of the 4x2 directional valve; and a second fluid line configuration of the 4x2 directional valve for providing a second connection to the first plurality of fluid lines while in the second position of the 4x2 directional valve. In an embodiment, the first directional valve may be configured to control flow through the first fluid line and through the second fluid line. According to another aspect of the invention, there is provided a method of operating a selective catalytic reduction system for an internal combustion engine, the selective catalytic reduction system comprising a storage tank configured to store a reducing agent, a pump assembly configured to pressurise the reducing agent, the pump assembly comprising an inlet and an outlet; and a dosing module configured to deliver the reducing agent to a vehicle exhaust system of the internal combustion engine. The method comprises driving the pump assembly through a pumping cycle comprising a pump phase and an inlet phase; and operating a valve arrangement to provide a connection between the storage tank, the pump assembly, and the dosing module by: (i) in a first operation mode corresponding to the pump phase of the pump assembly, operating the valve arrangement to connect an inlet of the pump assembly to the storage tank and to connect an outlet of the pump assembly to the dosing module; and, (ii) in a second operation mode corresponding to the return stroke phase of the pump assembly, operating the valve arrangement to connect the inlet of the pump assembly to the dosing module and to connect the outlet of the pump assembly to the storage tank. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. Brief Description of the Drawings In order that the invention may be more readily understood, preferred non-limiting embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which like features are assigned like reference numbers, and in which: Figure 1 schematically illustrates a known selective catalytic reduction system; Figure 2 schematically illustrates a selective catalytic reduction system in a first operation mode according to a first embodiment; Figure 3 schematically illustrates the selective catalytic reduction system of Figure 2 in a second operation mode; Figure 4 schematically illustrates a selective catalytic reduction system in a first operation mode according to a second embodiment; Figure 5 schematically illustrates the selective catalytic reduction system of Figure 4 in a second operation mode; Figure 6 schematically illustrates a selective catalytic reduction system in a first operation mode according to a third embodiment; Figure 7 schematically illustrates the selective catalytic reduction system of Figure 6 in a second operation mode; Figure 8 schematically illustrates a selective catalytic reduction system in a first operation mode according to a fourth embodiment; and Figure 9 schematically illustrates the selective catalytic reduction system of Figure 8 in a second operation mode. Detailed Description of Embodiments of the Invention Embodiments relate to a selective catalytic reduction (SCR) system comprising a valve arrangement configured to switch between operational modes such that the SCR system is capable of delivering reducing agent into a vehicle exhaust system of an internal combustion engine and aerating the SCR system to purge any reducing agent in the components and / or passages of the SCR system using a single pump assembly. Advantageously, the number of pump components required to operate the SCR system can therefore be reduced, increasing the compactness and cost effectiveness of the SCR system when compared to known SCR systems. The SCR system described herein is intended for use in a vehicle with an internal combustion engine, such as a diesel internal combustion engine. However, it should be appreciated that the SCR system may be suitable for other uses, including operating with other types of engines that produce exhaust gases. To provide context, Figure 1 shows in schematic form a simplified conventional SCR system 1 for use with an internal combustion engine that utilizes a dual pump configuration and may be used for passenger and low duty vehicle applications. The SCR system 1 includes a storage tank 2 for storing a fluid or liquid reducing agent, a pump module 3, a dosing module 4 (referred to as the doser), and a dosing module control unit 5. The doser 4 is configured to spray the reducing agent into a vehicle exhaust system 13 of the associated internal combustion engine. The tank 2 is fluidly connected to the pump module 3 via an output fluid line OL and an input fluid line IL. Reducing agent can pass out of the tank 2 through the output line OL to the pump module 3 via a filter 6 and a first seal 7a, and can pass back into the tank 2 from the pump module 3 through the input fluid line IL via a second seal 7b. The pump module 3 includes a first pump 10 placed upstream of the doser 4 and a second pump 11 placed downstream of the doser 4. The first and second pumps 10, 11 shown in Figure 1 may be diaphragm pumps which may be disposed in parallel within the SCR system 1. The pump module 3 includes a first pulsation damper 8a and a second pulsation damper 8b which smooth and regulate the flow of reducing agent out of and into the pump module 3 from the tank 2. Output check valves 9a and input check valves 9b ensure the reducing agent travels along the intended direction within the pump module 3 depending on the pump module’s operation. The output and input lines OL, IL of the pump module 3 are fluidly connected to the doser 4 via a third seal 7c and a third damper 8c. The output and input lines OL, IL may share a portion of fluid line for connecting to the doser 4, for example as illustrated in Figure 1, or may be separate fluid lines in accordance with the implementation of the SCR system 1. The control unit 5 is electrically connected to the pump module 3 and the doser 4 via control lines 12 for controlling the operation of the SCR system 1. In operation, the control unit 5 activates the primary pump 10 while the vehicle is in use. The primary pump 10, when activated, extracts reducing agent from the tank 2 along the output line OL for pressurization within the primary pump 10 and delivers the pressurized reducing agent to the doser 4. The doser 4 then delivers the pressurized reducing agent into the vehicle exhaust 13. When the vehicle is not in use, the secondary pump 11 is activated to pull any residual reducing agent from the components of the SCR system 1 back through the input line IL to the tank 2. The dual pump configuration enables the SCR system 1 to supply reducing agent to the vehicle exhaust 13 for the conversion of nitrogen oxides into water and nitrogen gas and to purge reducing agent from the SCR system 1 to prevent reducing agent from freezing within the SCR system 1. Separate dedicated components for each pump 10, 11 of the dual pump configuration, such as pulsation dampers 8 and check valves 9, are required in order to facilitate the operation of the SCR system 1. These components require physical space to be installed and each pump 10, 11 requires separate control lines 12 for connection to the control unit 5, increasing the overall size, complexity, and cost of the SCR system 1. The embodiments described herein relate to a compact and cost effective SCR system for an internal combustion engine of a vehicle, and particularly for diesel internal combustion engines. The SCR system may comprise a storage tank for storing a fluid or liquid reducing agent, a pump assembly (referred to as the pump) capable of pressurising the reducing agent, a dosing module (referred to as the doser) capable of delivering, injecting, or spraying the reducing agent into a vehicle exhaust system of the associated internal combustion engine, and a valve arrangement capable of providing a fluid connection between the storage tank, the pump assembly, and the doser. The SCR system may be used for passenger and low duty vehicle applications, for example, or other types of applicable vehicle applications. The valve arrangement comprises at least one directional valve, for example a directional solenoid or switching valve, capable of switching the SCR system between at least two operational modes. In a first mode of operation, the valve arrangement is operable to connect an inlet of the pump assembly to the tank and connects an outlet of the pump assembly to the doser. In general terms, in operation reducing agent is drawn from the tank, pressurised by the pump, and delivered to the doser for injection or spraying into the vehicle exhaust system. In a second mode of operation, the valve arrangement is operable to connect the inlet of the pump to the doser and the outlet of the pump to the tank. In the second mode of operation, any reducing agent in the SCR system is extracted from the components of the SCR system by the pump and flows back to the tank for storage. The first operation mode may correspond to when the vehicle is in use and / or is actively producing exhaust gases or fumes, and thus when the doser is operable to deliver reducing agent to the exhaust system. The second operation mode may correspond to when the vehicle is not in use and / or is not actively producing exhaust gases or fumes. In this manner, the SCR system is advantageously able use a single pump to deliver reducing agent to a vehicle exhaust system for the conversion of nitrogen oxides to water and nitrogen gas, and, by adjusting the operation mode of the valve arrangement, switch to purge the components of the SCR system of any residual reducing agent to prevent the freezing of the reducing agent within the SCR system. The number of pump components required to operate the system can therefore be reduced when compared to known SCR systems, such as the SCR system 1 of Figure 1 for example, thus reducing the system complexity and associated cost and allowing the SCR system to be packaged in a compact manner. It shall be appreciated that the embodiments described herein may take various forms for this purpose and may include, amongst other features, an associated or dedicated control system for controlling or monitoring the operation of the SCR system in response to a respective command signal (which may be generated in response to a change in the vehicle’s operation). The pump assembly of the SCR system may be a reciprocating piston or diaphragm delivery pump, however it will be appreciated that other types of pumps, for example which feature positive displacement with appropriate flow and suction characteristics, may be equally applicable. The valve arrangement may comprise at least one directional solenoid or switching valve operable to switch between a first position corresponding to the first operation mode and a second position corresponding to the second operation mode. The at least one directional valve may be activated or energized via a single control channel or line connected to the associated control system when changing between operation modes. For example, the at least one directional valve of the valve arrangement may be in a non-activated or non-energized state when in the first operation mode and may be activated or energized when in the second operation mode, or vice-versa. The reducing agent may be AdBlue®, however it will be appreciated that other reducing agents may be equally applicable. Examples of the SCR system are provided in Figures 2 to 9, which shall now be described. It shall be noted that some counterpart features of each example are assigned similar reference numbers, but incremented by 20 moving from one example to the next. It shall additionally be appreciated that various changes and modifications can be made to the SCR systems of Figures 2 to 9 without departing from the scope of the present invention. Figure 2 illustrates an exemplary example of a SCR system 20 in a first system mode, the SCR system 20 being for use with an internal combustion engine of an associated vehicle according to a first embodiment. The SCR system 20 may comprise a storage tank 22 for storing a reducing agent, a valve arrangement comprising a first directional valve 26 and a second directional valve 34, a pump 30, and a doser 36 for delivering reducing agent into a vehicle exhaust system 38 of the internal combustion engine. An associated control unit (not shown) is electrically connected to the SCR system 20 for monitoring and controlling its operation. In this example, the first and second valves 26, 34 may be capable of providing a connection between one or more different fluid lines, passages, pipes or the like depending on the operation mode of the valve arrangement. For example, the first valve 26 may be a 3x2 directional solenoid valve, whereby the first valve 26 is capable of connecting to three different fluid lines via three ports and has two internal fluid line configurations. The second valve 34 may be a 4x2 directional solenoid valve, whereby the second valve 34 is capable of connecting to four different fluid lines via four ports and has two internal fluid line configurations. The first and second valves 26, 34 are each capable of switching between two different positions, whereby upon activation the first and second valves 26, 34 switch from their respective first internal fluid line configuration to their respective second internal fluid line configuration so as to change the connection between the associated fluid lines, or vice-versa. A first port 23 of the tank 22 may be connected to the first valve 26 via a fluid line A1. A filter 24 may be disposed in the fluid line A1 to filter the reducing agent drawn from the tank 22. The first valve 26 may be connected to an inlet 29 of the pump 30 via a fluid line A2. A first check valve 28 may be disposed in the fluid line A2 to ensure a correct flow direction through the fluid line A2. An outlet 31 of the pump 30 may be connected to the second valve 34 via a fluid line B1. A second check valve 32 may be disposed in the fluid line B1 to ensure a correct flow direction through the fluid line B1. The second valve 34 may be connected to the doser 36 via a fluid line B2, to the first valve 26 via a fluid line A3 / B3, and also to a second port 39 of the tank 22 via a fluid line B4. The first and second valves 26, 34 shown in Figure 2 are in a first operation mode. In this mode of operation, the first valve 26 is positioned such that the ports of the first valve 26 connect the fluid line A1 to the fluid line A2, and the second valve 34 is positioned such that the ports of the second valve 34 connect the fluid line B1 to the fluid line B2, thereby connecting the inlet 29 of the pump 30 to the first port 23 of the tank 22 and the outlet 31 of the pump 30 to the doser 36. In this first operation mode, the second port 39 of the tank 22 is not connected to the other components of the SCR system 20. This defines the first mode of operation of the first and second valves 26, 34 whereby reducing agent is able to flow from the tank 22 to the pump 30 for pressurisation, and, at the required pressure level, is able to flow from the pump 30 to the doser 36 for delivery to the vehicle exhaust 38 to convert nitrogen oxides within the vehicle exhaust 38 into water and nitrogen gas. When operating the SCR system 20 in the first mode of operation, the pump 30 is activated to complete a pumping cycle including an inlet phase, whereby a vacuum is created within a pump chamber (not shown) of the pump 30 to draw fluid into the pump chamber, and a pump phase, whereby fluid in the pump chamber is pressurised. During the inlet phase, the pump 30 draws reducing agent from the first port 23 of the tank 22 via the fluid line A1, the filter 24, the first valve 26, the fluid line A2, and the first check valve 28 to the inlet 29 of the pump 30 for pressurization within the pump 30. The first check valve 28 is operable in dependence on the fluid pressure across it and, so, during this inlet phase, reducing agent is supplied to the pump 30. During the subsequent pump phase of the pump 30, reducing agent is pressurised by the pump 30 which then supplies the pressurized reducing agent from the outlet 31 of the pump 30 via the fluid line B1, the second check valve 32, the second valve 34, and the fluid line B2 to the doser 36 for delivery into the vehicle exhaust 38. Figure 3 shows the SCR system 20 of Figure 2 when in a second system mode. Here, the first and second valves 26, 34 shown in Figure 3 are in a second operation mode whereby the first and second valves 26, 34 are operable together by the control unit (i.e. are activated or energized, or vice-vera) to change the positions of the first and second valves 26, 34 from their respective first positions to the their respective second positions, whereby the ports of the first valve 26 connect the fluid line A3 / B3 to the fluid line A2 and the ports of the second valve 34 connect the fluid line B2 to the fluid line A3 / B3 and connects the fluid line B1 to the fluid line B4. In this configuration, the inlet 29 of the pump 30 is connected to the doser 36 and the outlet 31 of the pump 30 is connected to the second port 39 of the tank 22. The first port 23 of the tank 22 is not connected to the other components of the SCR system 20 in the second operation mode. As the pump 30 is driven through the inlet phase, a vacuum is created in the pump chamber of the pump 30 and a pressure differential is created across the first check valve 28 which causes the first check valve 28 to open. Any reducing agent residing within the components of the SCR system 20 is therefore sucked back through the fluid line B2, the second valve 34, the fluid line A3 / B3, the first valve 26, the fluid line A2, and the first check valve 28 and is drawn back to the inlet 29 of the pump 30. During the pump phase of the pump 30, the pump 30 pressurises any such residual reducing agent and then supplies the reducing agent from the outlet 31 of the pump 30. The pressure differential across the second check valve 32 causes the second check valve 32 to open and reducing agent is supplied to the second port 39 of the tank 22 via the fluid line B1, the second check valve 32, the second valve 34, and the fluid line B4. Any residual reducing agent that is exposed to the atmosphere at the doser 36 and / or that remains within the components of the SCR system 20 is drawn back into the tank 22. The removal of the reducing agent from the components of the SCR system 20 may cause a pressure differential to arise between the pressure of the exhaust gases at the vehicle exhaust 38 and the pressure within the components of the SCR system 20. To prevent this and to effectively depressurise the SCR system 20, the doser 36 may be temporarily opened as the reducing agent is drawn back into the tank 22 during the second operation mode. The doser 36 may be opened for a relatively short period of time in the same manner as if the doser 36 were injecting or spraying reducing agent into the vehicle exhaust 38. The removal of the reducing agent from the components of the SCR system 20 causes the external gases from the vehicle exhaust 38 to enter the SCR system 20 via the doser 36 and effectively replace the removed reducing agent within the components of the SCR system 20. The doser 36 may be subsequently closed to close off the SCR system 20 to the atmosphere. In this manner, reducing agent within the SCR system 20 is prevented from being exposed to low atmospheric temperatures and is thus prevented from freezing and causing damage to the SCR system 20 during the second operation mode. In summary, the SCR system 20 of Figures 2 and 3 is capable of a dual operation to supply reducing agent to the vehicle exhaust 38 and to aerate the components of the SCR system 20 to remove any reducing agent that may reside in them. The SCR system 20 may therefore comprise a first valve 26 connected to a first fluid line A2 between the tank 22 and the pump 30. The first valve 26 may comprise a first fluid line configuration of the first valve 26 (as illustrated in Figure 2) for connecting to a first plurality of fluid lines A1, A2, A3 / B3 while in a first position corresponding to the first operation mode, and a second fluid line configuration of the first valve 26 (as illustrated in Figure 3) for connecting to the first plurality of fluid lines A1, A2 A3 / B3 while in the second position corresponding to the second operation mode. The SCR system 20 may comprise a second valve 34 connected to a second fluid line B1 between the pump 30 and a dosing module 36. The second valve 34 may comprise a first fluid line configuration of the second valve 34 (as illustrated in Figure 2) for connecting to a second plurality of fluid lines B1, B2, A3 / B3, B4 while in a first position corresponding to the first operation mode, and a second fluid line configuration of the second valve 34 (as illustrated in Figure 3) for connecting to the second plurality of fluid lines B1, B2, A3 / B3, B4 while in the second position corresponding to the second operation mode. Figure 4 illustrates another exemplary example of a SCR system 40 in a first system mode, the SCR system 40 being for use with an internal combustion engine of an associated vehicle according to a second embodiment. The SCR system 40 may comprise a storage tank 42 for storing a reducing agent, a valve arrangement comprising a first directional valve 46, a second directional valve 54, a third directional valve 55, a supply pump 50, and a doser 56 for delivering reducing agent into a vehicle exhaust system 58 of the internal combustion engine. An associated control unit (not shown) is electrically connected to the SCR system 40 for monitoring and controlling its operation. In this example, the first, second, and third valves 46, 54, 55 may be capable of providing a connection between one or more different fluid lines, passages, pipes or the like depending on the operation mode of the valve arrangement. For example, each of the first and second valves 46, 54 may be a 3x2 directional solenoid valve, whereby the first and second valves 46, 54 are each capable of respectively connecting to three different fluid lines via three ports and each have two internal fluid line configurations. The first, second valves 46, 54 are each capable of switching between two different positions, whereby upon activation the first and second valves 46, 54 switch from their respective first internal fluid line configuration to their respective second internal fluid line configuration so as to change the connection between the associated fluid lines. The third valve 55 may be a 2x1 valve, whereby the third valve 55 is capable of connecting to two different fluid lines via two ports and has one internal fluid line configuration. The third valve 55 is capable of switching between two different positions, whereby activation of the third valve 55 to a first position corresponds to blocking a connection between the two different fluid lines and deactivation of the third valve 55 corresponds to a second position providing a connection between the two different fluid lines, or vice-versa. A first port 43 of the tank 42 may be connected to the first valve 46 via fluid line C1. A filter 44 may be disposed in the fluid line C1 to filter the reducing agent drawn from the tank 42. The first valve 46 may be connected to an inlet 49 of the pump 50 via a fluid line C2. A first check valve 48 may be disposed in the fluid line C2 to ensure a correct flow direction through the fluid line C2. An outlet 51 of the pump 50 may be connected to the second valve 54 via a fluid line D1 and the third valve 55 via a fluid line E1. The fluid line D1 and the fluid line E1 may have a common fluid line section D1 / E1 and it will be appreciated that fluid line D1 and fluid line E1 may be, for example, two separate fluid lines, a single fluid line with one or more branches, a plurality of individual fluid lines, or the like. A second check valve 52 may be disposed in the fluid line section D1 / E1 to ensure a correct flow direction through the fluid line section D1 / E1 and through the fluid lines D1 and E1. The second valve 54 may be connected to the doser 56 via a fluid line D2 and to the first valve 46 via a fluid line C3 / D3. The third valve 55 may be connected to a second port 59 of the tank 42 via a fluid line E2. The first, second, and third valves 46, 54, 55 shown in Figure 4 are in a first operation mode. In this mode of operation, the first valve 46 is positioned such that the ports of the first valve 46 connect the fluid line C1 to the fluid line C2, the second valve 54 is positioned such that the ports of the second valve 54 connect the fluid line D1 to the fluid line D2, and the third valve 55 is positioned such that the ports of the third valve 55 do not connect / block the connection from the fluid line E1 to the fluid line E2 and so does not connect the second port 59 of the tank 42 to the other components of the SCR system 40. In this manner, the inlet 49 of the pump 50 is connected to the first port 43 of the tank 42 and the outlet 51 of the pump 50 is connected to the doser 56. This defines the first mode of operation of the first, second, and third valves 46, 54, 55 where reducing agent is able to flow from the tank 42 to the pump 50 for pressurization, and, at the required pressure level, is able to flow from the pump 50 to the doser 56 for delivery to the vehicle exhaust 58 to convert nitrogen oxides within the vehicle exhaust 58 into water and nitrogen gas. When operating the SCR system 40 in the first mode of operation, the pump 50 is activated to complete a pumping cycle including an inlet phase, whereby a vacuum is created within a pump chamber (not shown) of the pump 50 to draw fluid into the pump chamber, and a pump phase whereby fluid in the pump chamber is pressurised. During the inlet phase, the pump 50 draws reducing agent from the first port 43 of the tank 42 via the fluid line C1, the filter 44, the first valve 46, the first check valve 48, and the fluid line C2 to the inlet 49 of the pump 50 for pressurization within the pump 50. The first check valve 48 is operable in dependence on the fluid pressure across it and, so, during this inlet phase, reducing agent is supplied to the pump 50. During the subsequent pump phase of the pump 50, reducing agent is pressurised by the pump 50 which then supplies the pressurized reducing agent from the outlet 51 of the pump 50 via the fluid line D1, the second check valve 52, the second valve 54, and the fluid line D2 for delivery to the doser 56 and into the vehicle exhaust 58. Figure 5 shows the SCR system 40 of Figure 4 when in a second system mode. Here, the first, second, and third valves 46, 54, 55 shown in Figure 5 are in a second operation mode whereby the first, second, and third valves 46, 54, 55 are operable together by the control unit (i.e. are activated or energized, or vice-versa) to change the positions of the first, second, and third valves 46, 54, 55 from their respective first positions to their respective second positions, whereby the ports of the first valve 46 connect the fluid line C3 / D3 to the fluid line C2, the ports of the second valve 54 connect the fluid line C3 / D3 to the fluid line D2, and the ports of the third valve 55 connect the fluid line E1 to the fluid line E2. In this configuration, the inlet 49 of the pump 50 is connected to the doser 56 and the outlet 51 of the pump 50 is connected to the second port 59 of the tank 42. The first port 43 of the tank 42 is not connected to the other components of the SCR system 40 in the second operation mode. As the pump 50 is driven through the inlet phase, a vacuum is created in the pump chamber of the pump 50 and a pressure differential is created across the first check valve 48 which causes the first check valve 48 to open. Any reducing agent residing within the components of the SCR system 40 is therefore sucked back through the fluid line D2, the second valve 54, the fluid line C3 / D3, the first valve 46, the fluid line C2, and the first check valve 48 to the inlet 49 of the pump 50. During the pump phase of the pump 50, the pump 50 pressurises any such residual reducing agent and then supplies the reducing agent from the outlet 51 of the pump 50. The pressure differential across the second check valve 52 causes the second check valve 52 to open and reducing agent is supplied to the second port 59 of the tank 42 via the fluid line E1, the second check valve 52, the third valve 55, and the fluid line E2. Any residual reducing agent that is exposed to the atmosphere at the doser 56 and / or that remains within the components of the SCR system 40 is drawn / pulled back into the tank 42. The removal of the reducing agent from the components of the SCR system 40 may cause a pressure differential to arise between the pressure of the exhaust gases at the vehicle exhaust 58 and the pressure within the components of the SCR system 40. To prevent this and to effectively depressurise the SCR system 40, the doser 56 may be temporarily opened as the reducing agent is drawn back into the tank 42 during the second operation mode. The doser 56 may be opened for a relatively short period of time in the same manner as if the doser 56 were injecting or spraying reducing agent into the vehicle exhaust 58. The removal of the reducing agent from the components of the SCR system 40 causes the external gases from the vehicle exhaust 58 enter the SCR system 40 via the doser 56 and effectively replace the removed reducing agent within the components of the SCR system 40. The doser 56 may be subsequently closed to close off the SCR system 40 to the atmosphere. In this manner, reducing agent within the SCR system 40 is prevented from being exposed to low atmospheric temperatures and is thus prevented from freezing and causing damage to the SCR system 40 during the second operation mode. In summary, the SCR system 40 of Figures 4 and 5 is capable of a dual operation to supply reducing agent to the vehicle exhaust 58 and to aerate the components SCR system 40 to remove any reducing agent that may reside in them. The SCR system 40 may therefore comprise a first valve 46 connected to a first fluid line C2 between the tank 42 and the pump 50. The first valve 46 may comprise a first fluid line configuration of the first valve 46 (as illustrated in Figure 4) for connecting to a first plurality of fluid lines C1, C2, C3 / D3 while in a first position corresponding to the first operation mode, and a second fluid line configuration of the first valve 46 (as illustrated in Figure 5) for connecting to the first plurality of fluid lines C1, C2, C3 / D3 while in the second position corresponding to the second operation mode. The SCR system 40 may comprise a second valve 54 connected to a second fluid line D1 between the pump 50 and a dosing module 56. The second valve 54 may comprise a first fluid line configuration of the second valve 54 (as illustrated in Figure 4) for connecting to a second plurality of fluid lines D1, D2, C3 / D3 while in a first position corresponding to the first operation mode, and a second fluid line configuration of the second valve 54 (as illustrated in Figure 5) for connecting to the second plurality of fluid lines D1, D2, C3 / D3 while in the second position corresponding to the second operation mode. The SCR system 40 may comprise a third valve 55 connected to a third fluid line E1 between the tank 42 and the pump 50. The third valve 55 may connect to a third plurality of fluid lines E1, E2 and may block the connection to the third plurality of fluid lines E1, E2 while in the first position, and may not block the connection to the third plurality of fluid lines E1, E2 while in the second position. The first, second, and third valves 46, 54, 55 may be operable together to switch the SCR system 40 between the first operation mode and the second operation mode. Figure 6 illustrates another exemplary example of a SCR system 60 in a first system mode, the SCR system 60 being for use with an internal combustion engine of an associated vehicle according to a third embodiment. The SCR system 60 may comprise a storage tank 62 for storing a reducing agent, a valve arrangement comprising a first directional valve 66 and a second directional valve 74, a supply pump 70, and a doser 76 for delivering reducing agent into a vehicle exhaust system 78. An associated control unit (not shown) is electrically connected to the SCR system 60 for monitoring and controlling its operation. In this example, the first and second valves 66, 74 may be capable of providing a connection between one or more different fluid lines, passages, pipes or the like depending on the operation mode of the valve arrangement. For example, the first and second valves 66, 74 may be 3x2 directional solenoid valves, whereby the first and second valves 66, 74 are each capable of respectively connecting to three different fluid lines via three ports and have two internal fluid line configurations. The first and second valves 66, 74 are each capable of switching between two different positions, whereby upon activation the first and second valves 66, 74 switch from their respective first internal fluid line configurations to their respective second internal fluid line configurations so as to change the connection between the associated fluid lines, or vice versa. A first port 63 of the tank 62 may be connected to the first valve 66 via a fluid line F1. A filter 64 is disposed in the fluid line F1 to filter the reducing agent drawn from the tank 62. The first valve 66 may be connected to an inlet 69 of the pump 70 via a fluid line F2. A first check valve 68 may be disposed in the fluid line F2 to ensure a correct flow direction through the fluid line F2. An outlet 71 of the pump 70 may be connected to the second valve 74 via a fluid line G1. A second check valve 72 may be disposed in the fluid line G1 to ensure a correct flow direction through the fluid line G1. The second valve 74 may be connected to the doser 76 via a fluid line G2 and to a second port 79 of the tank 62 via a fluid line F3. The fluid line F3 and the fluid line G2 may have a common fluid line section F3 / G2 and it will be appreciated that fluid lines F3 and G2 may be, for example, two separate fluid lines, a single fluid line with multiple branches, or a plurality of connected individual fluid lines without departing from the scope of the invention. The first and second valves 66, 74 shown in Figure 6 are in a first operation mode. In this mode of operation, the first valve 66 is positioned such that the ports of the first valve 66 connect the fluid line F1 to the fluid line F2, and the second valve 74 is positioned such that the ports of the second valve 74 connect the fluid line G1 to the fluid line G2, thereby connecting the inlet 69 of the pump 70 to the first port 63 of the tank 62 and the outlet 71 of the pump 70 to the doser 76. The second port 79 of the tank 62 is not connected to the other components of the SCR system 60. This defines the first mode of operation of the first and second valves 66, 74 where reducing agent is able to flow from the tank 62 to the pump 70 for pressurisation, and, at the required pressure level, is able to flow from the pump 70 for delivery to the vehicle exhaust 78 to convert nitrogen oxides within the vehicle exhaust 78 into water and nitrogen gas. When operating the SCR system 60 in the first mode, the pump 70 is activated to complete a pumping cycle including an inlet phase, whereby a vacuum is created within a pump chamber (not shown) of the pump 70 to draw fluid into the pump chamber, and a pump phase, whereby fluid in the pump chamber is pressurised. During the inlet phase, the pump 70 draws reducing agent from the first port 63 of the tank 62 via the fluid line F1, the filter 64, the first valve 66, the fluid line F2, and the first check valve 68 to the inlet 69 of the pump 70 for pressurization within the pump 70. The first check valve 68 is operable in dependence on the fluid pressure across it and, so, during this inlet phase, reducing agent is supplied to the pump 70. During the subsequent pump phase of the pump 70, reducing agent is pressurised by the pump 70 which then supplies the pressurized reducing agent from the outlet 71 of the pump 70 via the fluid line G1, the second check valve 72, the second valve 74, and the fluid line G2 for delivery to the doser 76 and into the vehicle exhaust 78. Figure 7 shows the SCR system 60 of Figure 6 when in a second system mode. Here, the first and second valves 66, 74 shown in Figure 7 are in a second operation mode whereby the first and second valves 66, 74 are operable together (i.e. are activated or energized, or vice-versa) by the control unit to change the positions of the first and second valves 66, 74 from their respective first positions to their respective second positions, whereby the ports of the first valve 66 connects the fluid line F3 to the fluid line F2 and the ports of the second valve 74 connects the fluid line G1 to the fluid line G3. In this configuration, the inlet 69 of the pump 70 is connected to the doser 76 and the outlet 71 of the pump 70 is connected to the second port 79 of the tank 62. The first port 63 of the tank 62 is not connected to the other components of the SCR system 60 in the second operation mode. As the pump 70 is driven through the inlet phase, a vacuum is created in the pump chamber of the pump 70 and a pressure differential is created across the first check valve 68 which causes the first check valve 68 to open. Any reducing agent residing within the components of the SCR system 60 is therefore sucked back through the fluid line F3, the first valve 66, the fluid line F2, and the first check valve 68 to the inlet 69 of the pump 70. During the pump phase of the pump 70, the pump 70 pressurises any such residual reducing agent and then supplies the residual reducing agent from the outlet 71 of the pump 70. The pressure differential across the second check valve 72 causes the second check valve 72 to open and reducing agent is supplied to the second port 79 of the tank 62 via the fluid line G1, the second check valve 72, the second valve 74, and the fluid line G3. Any residual reducing agent that is exposed to the atmosphere at the doser 76 and / or that remains within the components of the SCR system 60 is drawn back into the tank 62. The removal of the reducing agent from the components of the SCR system 60 may cause a pressure differential to arise between the pressure of the exhaust gases at the vehicle exhaust 78 and the pressure within the components of the SCR system 60. To prevent this and to effectively depressurise the SCR system 60, the doser 76 may be temporarily opened as the reducing agent is drawn back into the tank 62 during the second operation mode. The doser 76 may be opened for a relatively short period of time in the same manner as if the doser 76 were injecting or spraying reducing agent into the vehicle exhaust 78. The removal of the reducing agent from the components of the SCR system 60 causes the external gases from the vehicle exhaust 78 enter the SCR system 60 via the doser 76 and effectively replace the removed reducing agent within the components of the SCR system 60. The doser 76 may be subsequently closed to close off the SCR system 60 to the atmosphere. In this manner, reducing agent within the SCR system 60 is prevented from being exposed to low atmospheric temperatures and is thus prevented from freezing and causing damage to the SCR system 60 during the second operation mode. In summary, the SCR system 60 of Figures 6 and 7 is capable of a dual operation to supply reducing agent to the vehicle exhaust system 78 and to aerate the components SCR system 60 to remove any reducing agent that may reside in them. The SCR system 60 may therefore comprise a first valve 66 connected to a first fluid line F2 between the tank 62 and the pump 70. The first valve 66 may comprise a first fluid line configuration of the first valve 66 (as illustrated in Figure 6) for connecting to a first plurality of fluid lines F1, F2, F3 while in a first position corresponding to the first operation mode, and a second fluid line configuration of the first valve 66 (as illustrated in Figure 7) for connecting to the first plurality of fluid lines F1, F2, F3 while in the second position corresponding to the second operation mode. The SCR system 60 may comprise a second valve 76 connected to a second fluid line G1 between the pump 70 and a dosing module 76. The second valve 74 may comprise a first fluid line configuration of the second valve 74 (as illustrated in Figure 6) for connecting to a second plurality of fluid lines G1, F2 / G2, G3 while in a first position corresponding to the first operation mode, and a second fluid line configuration of the second valve 74 (as illustrated in Figure 7) for connecting to the second plurality of fluid lines G1, F2 / G2, G3 while in the second position corresponding to the second operation mode. The first and second valves 66, 74 may be operable together to switch the SCR system 60 between the first operation mode and the second operation mode. Figure 8 illustrates another exemplary example of a SCR system 80 in a first system mode, the SCR system 80 being for use with an internal combustion engine of an associated vehicle according to a fourth embodiment. The SCR system 80 may comprise a storage tank 82 for storing a reducing agent, a valve arrangement comprising a directional valve 86, a supply pump 90, and a doser 96 for delivering reducing agent into a vehicle exhaust system 98. An associated control unit (not shown) is electrically connected to the SCR system 80 for monitoring and controlling its operation. In this example, the valve 86 may be capable of providing a connection between one or more different fluid lines, passages, pipes or the like depending on the operation mode of the valve arrangement. For example, the valve 86 may be a 4x2 directional solenoid valve, whereby the valves 86 is connected to four different fluid lines via four ports and has two internal fluid line configurations. The valve 86 is capable of switching between two different positions, whereby upon activation the valve 86 switches from the first internal fluid line configuration to the second internal fluid line configuration so as to change the connection between the associated fluid lines, or vice versa. A port 83 of the tank 82 may be connected to the valve 86 via a fluid line 11. It will be appreciated that the port 83 of the tank 82 may be considered to be an inlet or an outlet of the tank 82 in accordance with the mode of operation of the valve arrangement of the present embodiment of the invention. A filter 84 may be disposed in the fluid line 11 to filter the reducing agent drawn from the tank 82. The valve 86 may be connected to an inlet 89 of the pump 90 via a fluid line I2. A first check valve 88 may be disposed in the fluid line I2 to ensure a correct flow direction through fluid line I2. An outlet 91 of the pump 90 may be connected to the valve 86 via a fluid line I3. A second check valve 92 may be disposed in the fluid line I3 to ensure a correct flow direction through fluid line I3. The valve 86 may be connected to the doser 96 via a fluid line I4. The valve 86 shown in Figure 8 is in a first operation mode. In this mode of operation, the valve 86 is positioned such that the ports of the valve 86 connect the fluid line 11 to the fluid line I2 and connect the fluid line I3 to the fluid line I4, thereby connecting the inlet 89 of the pump 90 to the port 83 of the tank 82 and the outlet 91 of the pump 90 to the doser 96. This defines the first mode of operation of the valve 86 where reducing agent is able to flow from the tank 82 to the pump 90 for pressurisation, and, at the required pressure level, is able to flow from the pump 90 for delivery to the vehicle exhaust 98 to convert nitrogen oxides within the vehicle exhaust 98 into water and nitrogen gas. When operating the SCR system 80 in the first mode, the pump 90 is activated to complete a pumping cycle including an inlet phase, whereby a vacuum is created within a pump chamber (not shown) of the pump 90 to draw fluid into the pump chamber, and a pump phase, whereby fluid in the pump chamber is pressurised. During the inlet phase, the pump 90 draws reducing agent from the port 83 of the tank 82 via the fluid line 11, the filter 84, the valve 86, the fluid line I2, and the first check valve 88 to the inlet 89 of the pump 90 for pressurization within the pump 90. The first check valve 88 is operable in dependence on the fluid pressure across it and, so, during this inlet phase, reducing agent is supplied to the pump 90. During the subsequent pump phase of the pump 90, reducing agent is pressurised by the pump 90 which then supplies the pressurized reducing agent from the outlet 91 of the pump 90 via the fluid line I3, the second check valve 92, the valve 86, and the fluid line I4 for delivery to the doser 96 and into the vehicle exhaust 98. Figure 9 shows the SCR system 80 of Figure 8 when in a second system mode. Here, the valve 86 shown in Figure 9 is in a second operation mode whereby the valve 86 is operated (i.e. is activated or energized, or vice-versa) by the control unit to change the position of the valve 86 from the first position to the second position, whereby the ports of the valve 86 connect the fluid line I4 to the fluid line I2 and connect the fluid line I3 to the fluid line 11. In this configuration, the inlet 89 of the pump 90 is connected to the doser 96 and the outlet 91 of the pump 90 is connected to the port 83 of the tank 82. As the pump 90 is driven through the inlet phase, a vacuum is created in the pump chamber of the pump 90 and a pressure differential is created across the first check valve 88 which causes the first check valve 88 to open. Any reducing agent residing within the components of the SCR system 80 is therefore sucked back through the fluid line I4, the valve 86, the fluid line I2, and the first check valve 88 to the inlet 89 of the pump 90. During the pump phase of the pump 90, the pump 90 pressurises any such residual reducing agent and then supplies the residual reducing agent from the outlet 91 of the pump 90. The pressure differential across the second check valve 92 causes the second check valve 92 to open and reducing agent is supplied to the port 83 of the tank 82 via the fluid line I3, the second check valve 92, the valve 86, the fluid line 11, and the filter 84. Any reducing agent that is exposed to the atmosphere at the doser 96 and / or that remains within the components of the SCR system 80 is drawn / pulled back into the tank 82. The removal of the reducing agent from the components of the SCR system 80 may cause a pressure differential to arise between the pressure of the exhaust gases at the vehicle exhaust 98 and the pressure within the components of the SCR system 80. To prevent this and to effectively depressurise the SCR system 80, the doser 96 may be temporarily opened as the reducing agent is drawn back into the tank 82 during the second operation mode. The doser 96 may be opened for a relatively short period of time in the same manner as if the doser 96 were injecting or spraying reducing agent into the vehicle exhaust 98. The removal of the reducing agent from the components of the SCR system 80 causes the external gases from the vehicle exhaust 98 enter the SCR system 80 via the doser 96 and effectively replace the removed reducing agent within the components of the SCR system 80. The doser 96 may be subsequently closed to close off the SCR system 80 to the atmosphere. In this manner, reducing agent within the SCR system 80 is prevented from being exposed to low atmospheric temperatures and is thus prevented from freezing and causing damage to the SCR system 80 during the second operation mode. In summary, the SCR system 80 of Figures 8 and 9 is capable of a dual operation to supply reducing agent to the vehicle exhaust system 98 and to aerate the components SCR system 80 to remove any reducing agent that may reside in them. The SCR system 80 may therefore comprise a first valve 86 connected to a first fluid line 12 between the tank 82 and the pump 90 and to a second fluid line 13 between the pump 90 and a dosing module 96. The first valve 86 may comprise a first fluid line configuration (as illustrated in Figure 8) for connecting to a first plurality of fluid lines 11,12,13,14 while in a first position corresponding to the first operation mode, and a second fluid line configuration (as illustrated in Figure 9) for connecting to the first plurality of fluid lines 11, I2, I3, I4 while in the second position corresponding to the second operation mode. The first valve 86 may be operable to switch the SCR system 80 between the first operation mode and the second operation mode. It will be appreciated by a person skilled in the art that the embodiments described above could be modified to take many alternative forms to that described herein, without departing from the scope of the appended claims. References used: 1 - Selective catalytic reduction system 2 - Storage tank 3 - Pump module 4 - Dosing module / doser 5 - Dosing module control unit 6 - Filter 7a, 7b, 7c- First, second, and third seals 8a, 8b, 8c- First, second, and third pulsation dampers 9a - Output check valves 9b - Input check valves 10 - Primary pump 11 - Secondary pump 12 - Control lines 13 - Vehicle exhaust system IL - Input fluid line OL - Output fluid line 20 - Selective catalytic reduction system 22 - Storage tank 23 - First port of storage tank 24 - Filter 26 - First directional valve 28 - First check valve 29 - Inlet of supply pump 30 - Supply pump 31 - Outlet of supply pump 32 - Second check valve 34 - Second directional valve 36 - Dosing module / doser 38 - Vehicle exhaust system 39 - Second port of storage tank A1, A2, A3 / B3 - Fluid lines of first directional valve B1, B2, A3 / B3, B4 - Fluid lines of second directional valve 40 - Selective catalytic reduction system 42 - Storage tank 43 - First port of storage tank 44 - Filter 46 - First directional valve 5 48 - First check valve 49 - Inlet of supply pump 50 - Supply pump 51 - Outlet of supply pump 52 - Second check valve 10 54 - Second directional valve 55 - Third directional valve 56 - Dosing module / doser 58 - Vehicle exhaust system 59 - Second port of storage tank 15 C1, C2, C3 / D3 - Fluid lines of first directional valve D1, D2, C3 / D3 - Fluid lines of second directional valve E1, E2 - Fluid lines of third directional valve 60 - Selective catalytic reduction system 20 62 - Storage tank 63 - First port of storage tank 64 - Filter 66 - First directional valve 68 - First check valve 25 69 - Inlet of supply pump 70 - Supply pump 71 - Outlet of supply pump 72 - Second check valve 74 - Second directional valve 30 76 - Dosing module / doser 78 - Vehicle exhaust system 79 - Second port of storage tank F1, F2, F3 - Fluid lines of first directional valve G1, G2, G3 - Fluid lines of second directional valve 35 80 - Selective catalytic reduction system 82 - Storage tank 83 - Port of storage tank 84 - Filter 86 - Directional valve 88 - First check valve 5 89 - Inlet of supply pump 90 - Supply pump 91 - Outlet of supply pump 92 - Second check valve 96 - Dosing module / doser 10 98 - Vehicle exhaust system 11, I2, I3, I4- Fluid lines of directional valve

Claims

1. A selective catalytic reduction system (20, 40, 60, 80) for an internal combustion engine, the selective catalytic reduction system (20, 40, 60, 80) comprising:a storage tank (22, 42, 62, 82) for storing a reducing agent;a pump assembly (30, 50, 70, 90) configured to pressurise the reducing agent, the pump assembly comprising an inlet (29, 49, 69, 89) and an outlet (31, 51, 71, 91);a dosing module (36, 56, 76, 96) configured to deliver the reducing agent to a vehicle exhaust system (38, 58, 78, 98) of the internal combustion engine; anda valve arrangement operable to provide a connection between the storage tank (22, 42, 62, 82), the pump assembly (30, 50, 70, 90), and the dosing module (36, 56, 76, 96);wherein, in a first operation mode, the valve arrangement is operable to connect the inlet (29, 49, 69, 89) of the pump assembly (30, 50, 70, 90) to the storage tank (22, 42, 62, 82) and to connect the outlet (31, 51, 71, 91) of the pump assembly (30, 50, 70, 90) to the dosing module (36, 56, 76, 96), andwherein, in a second operation mode, the valve arrangement is operable to connect the inlet (29, 49, 69, 89) of the pump assembly (30, 50, 70, 90) to the dosing module (36, 56, 76, 96) and to connect the outlet (31, 51, 71, 91) of the pump assembly (30, 50, 70, 90) to the storage tank (22, 42, 62, 82).

2. The selective catalytic reduction system (20, 40, 60, 80) of claim 1, wherein the valve arrangement comprises at least one directional valve operable to switch between a first position corresponding to the first operation mode and a second position correspond to the second operation mode.

3. The selective catalytic reduction system (20, 40, 60, 80) of claim 2, wherein:the at least one directional valve is operable to a non-energized state when in the first operation mode and is operable to an energized state when in the second operation mode; or the at least one directional valve is operable to an energized state when in the first operation mode and is operable to a non-energized state when in the second operation mode.

4. The selective catalytic reduction system (20, 40, 60, 80) of claim 2 or 3, wherein the valve arrangement comprises a first directional valve (26, 46, 66, 86) connected to a first fluid line (A2, C2, F2, I2) between the storage tank (22, 42, 62, 82) and the pump assembly (30, 50, 70, 90), the first directional valve (26, 46, 66, 86) being operable to switch between a first position of the first directional valve (26,46,66,86) and a second position of the first directional valve (26, 46, 66, 86).

5. The selective catalytic reduction system (20, 40, 60) of claim 4, wherein the first directional valve (26, 46, 66) comprises a first fluid line configuration of the first directional valve (26, 46, 66) for connecting to a first plurality of fluid lines while in the first position of the first directional valve (26, 46, 66), and a second fluid line configuration of the first directional valve (26, 46, 66) for connecting to the first plurality of fluid lines while in the second position of the first directional valve (26, 46, 66).

6. The selective catalytic reduction system (20, 40, 60) of claim 4 or claim 5, wherein the valve arrangement comprises a second directional valve (34, 54, 74) connected to a second fluid line (B1, D1, G1, I3) between the pump assembly (30, 50, 70) and the dosing module (36, 56, 76), the second directional valve (34, 54, 74) being operable to switch between a first position of the second directional valve (34, 54, 74) and a second position of the second directional valve (34, 54, 74).

7. The selective catalytic reduction system (20, 40, 60) of claim 6, wherein the second directional valve (34, 54, 74) comprises a first fluid line configuration of the second directional valve (34, 54, 74) for connecting to a second plurality of fluid lines while in the first position of the second directional valve (34, 54, 74), and a second fluid line configuration of the second directional valve (34, 54, 74) for connecting to the second plurality of fluid lines while in the second position of the second directional valve (34, 54, 74).

8. The selective catalytic reduction system (20, 40, 60) of any of claims 4 to 7, wherein the first and second directional valves (26, 34, 46, 54, 66, 74) are operable together to switch between the first operation mode and the second operation mode.

9. The selective catalytic reduction system (40) of any of claims 2 to 8, wherein the valve arrangement comprises a third directional valve (55) connected to a third fluid line (E1) between the pump assembly (50) and the storage tank (42), the third directional valve (55) being operable to switch between a first position of the third directional valve (55) and a second position of the third directional valve (55).

10. The selective catalytic reduction system (40) of claim 9, wherein the third directional valve (55) connects to a third plurality of fluid lines, and wherein the third directional switching valve (55) blocks a connection to the third plurality of fluid lines while in the first position of the third directional valve (55), and opens the connection to the third plurality of fluid lines while in the second position of the second directional valve (55).

11. The selective catalytic reduction system (40) of claim 9 or 10, wherein the third directional valve (55) is operable together with the first and second directional valves (26, 34, 46, 54, 66, 74) to switch between the first operation mode and the second operation mode.

12. The selective catalytic reduction system (80) of claim 4, wherein the first directional valve (86) comprises a first fluid line configuration of the first directional valve (86) for providing a first connection to a first plurality of fluid lines while in the first position of the first directional valve (86), and a second fluid line configuration of the first directional valve (86) for providing a second connection to the first plurality of fluid lines while in the second position of the first directional valve (86).

13. The selective catalytic reduction system (80) of claim 12, wherein the first directional valve (86) is configured to control flow through the first fluid line (I2) and through a second fluid line (I3) between the pump assembly (90) and the dosing module (96).

14. The selective catalytic reduction system (20, 40, 60, 80) of any preceding claim, wherein the dosing module (36, 56, 76, 96) is operable to be temporarily opened during the second operation mode.

15. A method of operating a selective catalytic reduction system (20, 40, 60, 80) for an internal combustion engine, the selective catalytic reduction system (20, 40, 60, 80) comprising a storage tank (22, 42, 62, 82) configured to store a reducing agent, a pump assembly (30, 50, 70, 90) configured to pressurise the reducing agent, the pump assembly comprising an inlet (29, 49, 69, 89) and an outlet (31, 51, 71, 91); and a dosing module (36, 56, 76, 96) configured to deliver the reducing agent to a vehicle exhaust system (38, 58, 78, 98) of the internal combustion engine; the method comprising:driving the pump assembly through a pumping cycle comprising a pump phase and an inlet phase; andoperating a valve arrangement to provide a connection between the storage tank (22, 42, 62, 82), the pump assembly (30, 50, 70, 90), and the dosing module (36, 56, 76, 96) by:(i) in a first operation mode corresponding to the pump phase of the pump assembly, operating the valve arrangement to connect an inlet (29, 49, 69, 89) of the pump assembly (30, 50, 70, 90) to the storage tank (22, 42, 62, 82) and to connect an outlet (31, 51, 71, 91) of the pump assembly (30, 50, 70, 90) to the dosing module (36, 56, 76, 96), and(ii) in a second operation mode corresponding to the return stroke phase of the pump assembly, operating the valve arrangement to connect the inlet (29, 49, 69, 89) of the pump assembly (30, 50, 70, 90) to the dosing module (36, 56, 76, 96) and to connect the outlet (31, 51, 71, 91) of the pump assembly (30,5 50, 70, 90) to the storage tank (22, 42, 62, 82).

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