Fluid delivery system

#The present invention relates to a fluid delivery system for delivering a metered dose of fluid from a supply tank to a downstream vessel or chamber. In particular, but not exclusively, the invention relates to fluid delivery system including a pump apparatus for delivering a metered dose of reagent fluid, such as urea, to an exhaust gas pipe of an internal combustion engine or other equivalent device. The invention also relates to a method of determining the total volumetric delivery of a fluid to the downstream vessel or chamber and/or to a method of determining a remaining level of said fluid in the fluid supply tank.

#Internal combustion engines emit undesirable pollutants in their exhaust stream. One such pollutant is nitrogen oxides, comprising nitrogen monoxide and nitrogen dioxide (hereinafter referred to simply as “NOx”). NOx is generated from automobile engines such as diesel engines, and other combustion devices. Accordingly, exhaust system devices are coupled to the engine to limit and/or remove the pollutants from the exhaust system. Technologies have been and continue to be developed to attenuate these emissions.

#NOx may be cleaned from exhaust gases of internal combustion engines through the use of catalysis. In addition to removing NOx, other catalysts may be employed to also remove unburned hydrocarbons (HC) and carbon monoxide (CO). When the engine is operated with a lean air/fuel ratio, the catalyst is efficient at removing the HCs and COs because of the extra oxygen in the exhaust gas. However, the extra oxygen tends to inhibit the removal of NOx.

#The invention will now be described, by way of example only, with reference to the following Figures in which:

#FIG. 1 is a schematic illustration of an exhaust system including a reagent delivery system in accordance with a first embodiment of the present invention;

#FIG. 2 is a cross sectional view of a metering pump for use in the reagent delivery system of FIG. 1;

#Referring to FIG. 1, an exhaust system for an internal combustion engine includes an exhaust pipe 10 having an inlet end 12 in communication with an exhaust of an engine (not shown) and an outlet end 14 in communication with atmosphere. The exhaust pipe is provided with a diesel particulate filter, located approximately at position X, and a selective catalytic reduction (SCR) catalyst located approximately at position Y. A mixing section 16, intermediate the particulate filter and the SCR catalyst, accommodates a nozzle of an injection device 18 for delivering a reagent into the mixing section 16 of the exhaust pipe 10.

#The injection device 18 is positioned so as to deliver an atomised spray of reagent to the exhaust flow as it flows between the filter and the catalyst. A pump apparatus in the form of a metering pump 20 delivers a known quantity of reagent to the injection device 18 through a supply pipe 22 in a known time under the control of an engine control unit (ECU) 24. The ECU 24 includes a microprocessor 26 loaded with an algorithm to control operation of the metering pump 20 in dependence on various operating parameters. The metering pump 20 communicates with the supply tank 28 of reagent fluid via an inlet supply pipe 30. Typically, the reagent is aqueous urea. In other systems (not shown) the diesel particulate filter is downstream of the SCR catalyst, in which case the metering pump 20 delivers reagent to a mixing section upstream of the diesel particulate filter.

#The metering pump 20 is shown in more detail in FIG. 2, and includes a pump plunger 32 which is slidable within a stepped bore of a pump housing 34 under the control of a solenoid-controlled actuator, referred to generally as 36. The actuator 36 includes a solenoid and stator (not visible), to which a current is supplied to generate a magnetic field, and an armature 38 coupled to the pump plunger 32 at its upper end. The solenoid and stator are housed within a solenoid housing 40 which abuts the pump housing 34 at its upper end. The frame and structure surrounding the solenoid, the upper end of the pump plunger 32 and a stationary magnetic pole (not shown) provide a flux path to focus the magnetic field. The armature 38 reacts to the magnetic field and is attracted to the stationary pole, thereby causing the pump plunger 32 to move within the pump housing 34.