Method of determining operation of an SCR reductant doser

Abstract

In a selective catalytic reductant dosing system including a reductant injector adapted to inject liquid reductant into an exhaust line, a method of analyzing flow of reductant through the injector includes determining a measure of the temperature of the injector prior to activation of the injector. The method also includes activating the injector and determining a measure of the temperature of the injector subsequent to activation of the injector. The method also includes analyzing the flow of reductant through the injector consequential to the activation by analyzing changes in the measure of temperature of the injector prior to activation and the measure of temperature of the injector subsequent to activation.

Claims

1. In a selective catalytic reductant dosing system including a reductant injector adapted to inject liquid reductant into an exhaust line, a method of analyzing flow of reductant through the reductant injector comprising: i) determining a measure of the temperature of the reductant injector prior to activation of the reductant injector; ii) activating the reductant injector; iii) determining a measure of the temperature of the reductant injector subsequent to activation of the reductant injector; iv) analyzing the flow of reductant through the reductant injector consequential to activation of the reductant injector by analyzing a change in the measure of temperature prior to activation of the reductant injector and the measure of temperature of the reductant injector subsequent to activation of the reductant injector.

2. A method as claimed in claim 1, wherein in step iv) the flow is analyzed by comparing the changes with expected changes in the measure of temperature subsequent to activation of the reductant injector.

3. A method as claimed in claim 1, wherein step iv) comprises comparing a profile of the measure of temperature subsequent to activation of the reductant injector with expected or known profiles of the measure of temperature subsequent to activation of the reductant injector.

4. A method as claimed in claim 1, where in step iv) the change in the measure of temperature prior to activation of the reductant injector and the measure of temperature of the reductant injector subsequent to activation of the reductant injector at a time-point prior to activation and a point subsequent to activation is determined.

5. A method as claimed in claim 4, wherein the change in the measure of temperature is compared with an expected change of the measure of temperature subsequent to activation.

6. A method as claimed in claim 5, wherein the change in the measure of temperature is determined from the difference between a maximum value and a minimum value of the measure of temperature.

7. A method as claimed in claim 1, wherein from steps i) and iii) a gradient in the measure of temperature with respect to time is determined.

8. A method as claimed in claim 7, wherein the gradient is compared with an expected gradient.

9. A method as claimed in claim 7, wherein the gradient is determined over a time period from the maximum value and the minimum value of the measure of temperature or vice versa.

10. A method as claimed in claim 1, wherein the reductant injector is cooled by a cooling system comprising a cooling fluid passing adjacent to the reductant injector.

11. A method as claimed in claim 1, where the measure of temperature of the reductant injector is determined by a temperature sensor adjacent to the reductant injector, injector coil, or the temperature of coolant.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The invention will now be described by way of example and with reference to the following figures of which:

(2) FIG. 1 shows plot of voltage across, and current through, the coil of a solenoid actuated urea injector during an injection event;

(3) FIG. 2 shows the temperature profile of a coil of a urea injector over time with respect to a urea injection event (top) and the bottom plot shows the profile of urea flow from/through the injector.

(4) FIG. 3 compares the temperature profile of a reductant injector during an operating cycle to one which is blocked to one that is operating normally;

(5) FIG. 4 compares the temperature profile of a coil for an injector operating normally and one which is partially blocked; and,

(6) FIG. 5 compares the temperatures slopes (gradients) of temperature profiles of a normally operating injector and that of a blocked injector, during an injection cycle.

PRIOR ART

(7) It is known to detect and analyse injection operation of a SCR injector using the feedback current signal during an injection event. This can be performed by looking at the current flowing through the solenoid actuator coil of the injector to detect a valve movement. For example the point of inflection in the injector solenoid drive waveform will give information of valve events.

(8) It is also known to be able to detect the temperature of a SCR injector coil using the feedback current from the injector coil terminals during an injection event. This method analyses the current flowing through the injector coil to estimate the coil resistance. The temperature is calculated based on the change in resistance. Typically the current for the latter method is determined at the point of maximum current. FIG. 1 which shows plot of voltage across, and current through, the coil of a solenoid actuated urea injector.

DETAILED DESCRIPTION OF THE INVENTION

(9) In a simple example according to one aspect of the invention, the diagnosis of flow of reductant such as urea through a urea injector, is determined by obtaining a measure of, or analyzing the change in, temperature (or temperature profiles) of the SCR coil or injector as a result of the cooling effect of reductant such as urea flowing through the injector, (e.g. during an injection event) and comparing this with know or expected temperature of the coil (or temperature profiles during an injection event).

(10) The temperature may be determined by provision of a temperature sensor located on or adjacent to the injector (particularly the injector coil). Alternatively an estimate may be provided by measuring the temperature of coolant flowing in the injector cooling system e.g. flowing in a cooling jacket.

(11) FIG. 1 which shows plot of voltage across, and current through, the coil of a solenoid actuated urea injector.

(12) FIG. 2 shows the temperature profile of a coil of a urea injector over time with respect to a urea injection event (top) and the bottom plot shows the profile of urea flow from/through the injector. When urea is injected, urea flows through the injector, thereby cooling the coil, as seem in the figure.

(13) The injector may be cooled by coolant flowing through a coolant jacket. When no urea is flowing in the injector, the injector coil is heated to the temperature of the coolant flowing in the coolant jacket.

(14) It is to be noted that the temperature of the supply of the reductant such as urea to the injector, (i.e. incoming urea temperature) is usually at a different temperature (usually lower) than the temperature of the coil or coolant.

(15) FIG. 3 compares the temperature profile of a injector which has become blocked (e.g, has a blocked nozzle) to one that is operating normally, during an operating cycle, i.e. injection event.

(16) As can be seen, assuming the urea/reductant supplied to the injector is cooler than the injector, with the injector, the cooling effect will not be observed.

(17) Further, it is also possible to detect a partially blocked nozzle by a virtue of a reduced cooling flow of the urea. FIG. 4 compares the temperature profile of a injector coil for an injector operating normally and one which is partially blocked (during an injection cycle). As can be seen, there is a reduced cooling effect from the urea/reductant flow where there is a blocked nozzle.

(18) The skilled person would understand there are various ways in which the temperature profile of the coil may be used to determine whether there is an impedance to flow.

(19) One measure may be determining the absolute temperature drop between two points such as the maximum temperature and the minimum temperature; this is shown in FIG. 5 for two cases, B) an injector operating normally and A) an injector with a (partially/fully) blocked nozzle. The absolute temperature drop for both cases subsequent to an injection event (or injector activation as no urea may be injected with a fully blocked nozzle) is shown by arrows B and A respectively.

(20) In an alternative method the change in temperature of an injector with time (i.e. slope) is determined. This method may be performed at selected or suitable time points, and is preferably performed from the point during an injection/activation cycle from maximum temperature to minimum temperature i.e. looking at the slope from the maximum temperature to the minimum temperature in an injection cycle as shown in FIG. 5; the slopes for unblocked or partially blocked injector temperature are shown by B and A respectively.

(21) In an alternative method, a modelled coil temperature based on heat flow in and out of the coil may be used, and this compared to the measured coil temperature from the current in the injector.