WO2016173774A1

WO2016173774A1 - Urea dosing method for vehicle exhaust systems

Info

Publication number: WO2016173774A1
Application number: PCT/EP2016/056116
Authority: WO
Inventors: Martin Sykes
Original assignee: Delphi International Operations Luxembourg S.À R.L.
Priority date: 2015-04-28
Filing date: 2016-03-21
Publication date: 2016-11-03
Also published as: GB201507156D0

Abstract

A method of controlling the dosing of a liquid reductant, supplied from a pressurised supply to a solenoid actuated reductant injector for injection into a vehicle exhaust system comprising: a) obtaining a voltage and/or current signal across the actuator solenoid during its activation; b) analysing said signal and determining an opening and/or closing delay from said signal; c) correlating the results of step b) with a pre-stored relationship relating the injector reductant supply pressure to said opening and/or closing delay; and e) controlling the dosing of reductant depending on said determined pressure from step d).

Description

Urea Dosing Method for Vehicle Exhaust Systems

Field of the Invention

This disclosure relates to a urea dosing method system for use in exhaust systems of vehicles.

Background to the invention

Urea injection systems are known for use in vehicle exhaust systems. These are utilised in order to inject urea in an exhaust line upstream of a catalytic unit. The injected urea is converted to ammonia which is used to convert NO_x gases. Usually the urea is injected by using a solenoid actuated injector, supplied with urea under pressure. Such an injector may be water-cooled. It is important to ensure correct dosage of urea in order to provide optimum efficiency of the conversion of NO_x gases. In order to accurately control the dosing quantity of urea, accurate knowledge of the urea pressure supplied to the injector is required. Typically therefore, a pressure sensor is required which is usually located in the urea feed line. However the use of a pressure sensor increases cost.

It is an object of the invention to overcome these problems by providing a method of accurate dosing of urea, by determining/estimating the urea pressure without the use of a pressure sensor.

Statement of the invention

In a first aspect is provided a method of controlling the dosing of a liquid reductant, supplied from a pressurised supply to a solenoid actuated reductant injector for injection into a vehicle exhaust system comprising: a) obtaining a voltage and/or current signal across the actuator solenoid during its activation; b) analysing said signal and determining an opening and/or closing delay from said signal; c) correlating the results of step b) with a pre-stored relationship relating the injector reductant supply pressure to said opening and/or closing delay; and e) controlling the dosing of reductant depending on said determined pressure from step d).

The opening or closing delay is preferably determined by detecting a glitch in said signal, indicative of a valve movement event. In step c) the pre-stored relationship may correlate time-to-glitch or opening delay with the reductant supply pressure to the injector. The reductant may be urea.

The method may include additionally determining one or more parameters of injector supply voltage and determining the reductant pressure based on this parameter additionally.

The method may include determining/estimating the electrical resistance of the injector and determining the reductant pressure based on this parameter additionally.

The resistance may be determined from determining supply voltage and measured current. The method may be performed at a reductant supply pressure substantially close to zero.

Brief Description of Drawings

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

Figure 1 shows a diagrammatic representation of a urea injection system;

Figure 2 shows a diagrammatic representation of a urea injection system that can be used according to aspects of the invention;

Figure 3 shows a schematic representation of a urea injector;

Figure 4 shows the profiles of current through a urea injector solenoid actuator when dispensing a quantity of urea, for a low pressure and high pressure supply;

Figure 5 shows the current profiles at varying pressures; and

Figure 6 shows how the time to the glitch (opening delay) varies with urea pressure.

Description of Detailed Examples

Figure 1 shows a diagrammatic representation of a urea injection system showing a water cooled solenoid injectorl , supplied with urea via a high temperature feed line 2. The high temperature feed line is supplied from urea reservoir 3 by means of pump 4 with a bottom mount UDM (Urea Delivery Module) which may include a heater, filter 5, level sensor, temperature sensor, and pressure sensor 6. The urea pressure sensor 6 is used to control injection. Figure 2 shows a diagrammatic representation of a urea injection system that can be used according to aspects of the invention. This is identical to the figure 1 representation except that it does not include a pressure sensor 6.

Figure 3 shows a urea injector 1. The injector includes a solenoid and electric coil 9 adapted to move a valve 7 so as to lift a needle off a seat so as to allow urea under pressure, from a pressurised urea supply line to be dispensed into the exhaust system. The solenoid in the urea injector directly controls a nozzle valve 7 which is held closed by the force of a spring and the urea pressure. Power is supplied to the solenoid via a connector 10 . The solenoid is activated by supplying a drive pulse. The length drive pulse dictates the quantity of urea dispensed. The force required to open the injector is proportional to the urea pressure plus the spring pre load. The magnetic force generated by the solenoid increases after the start of an electrical drive pulse, and needs to overcome the urea supply pressure. Hence it will take a higher current and therefore a longer time to open the injector at higher urea pressures than at lower pressures.

It is possible to detect the start of injection by measuring and analyzing the injector drive current. Figure 4 shows the profiles of current through the solenoid actuator when dispensing a quantity of urea for a low pressure (B) and high pressure (A) urea supply. It also shows the change in opening delay (start of electrical pulse to nozzle opening). The current is ramps up in an pull in phase before being reduced and controlled by PWM (Pulse width modulation) in the hold phase. During the pull in phase there occurs an observable glitch shown by the locations of X in both curves. This glitch is caused by changes in the magnetic circuit when the valve moves (open) after overcoming spring and other forces (such as urea supply pressure). This therefore represents a measure of the opening delay as shown by the horizontal arrows in the figure. The higher the opening delay corresponed with higher urea supply pressure. Thus if the opening delay is determined; this can be correlated with the urea pressure.

Figure 5 shows the current profiles at varying pressures. The glitch on the curves occur in the same general area; however there are more precise differences in when they occur.

Figure 6 shows in higher resolution how the time to the glitch (opening delay) varies with urea pressure. According to one embodiment such relationship may be stored (e.g. in an engine ECU) as maps. In simple embodiments the current (or voltage across the solenoid) is measured and analysed and the glitch detected. The time taken to the glitch from the start of the activation pulse is determined and used to estimate the urea pressure by suitable correlation techniques e.g. by a look-up table/maps with information relating time to glitch with urea pressure (figure 6). One issue is that there may be injector to injector variations (i.e. the rate of magnetic force rise may vary between injectors, friction, spring rate, spring preload....), therefore in a preferred embodiment it is advantage to measure the opening delay for a known pressure condition such as zero pressure. If the opening delay is measured at zero pressure, the time taken for the magnetic force to reach the pre load force can be determined. Then when pressure is applied the additional time to reach the opening force is entirely due to the additional pressure. This increases the accuracy of the pressure estimation.

In further embodiments the method compensates for variations in supply voltage. This parameter can be measured by the control unit. In further embodiments the method can compensate for injector resistance (which will vary as a function of injector temperature). Injector resistance can be determined by determining the supply voltage and measuring the injector current at the point where the current is stable.

The nozzle closing delay may also be impacted by the change in supply pressure. This time the closing delay will reduce with increased pressure. In a refined embodiment, the closing delay may used alone or to determine supply pressure or in combination with the change in opening delay to increase the accuracy of the pressure estimation.

Claims

1. A method of controlling the dosing of a liquid reductant, supplied from a pressurised supply to a solenoid actuated reductant injector for injection into a vehicle exhaust system comprising: a) obtaining a voltage and/or current signal across the actuator solenoid during its activation; b) analysing said signal and determining an opening and/or closing delay from said signal; c) correlating the results of step b) with a pre-stored relationship relating the injector reductant supply pressure to said opening and/or closing delay; and d) controlling the dosing of reductant depending on said determined pressure from step c).

2. A method as claimed in claim 1 where said opening or closing delay is determined by detecting a glitch in said signal, indicative of a valve movement event.

3. A method as claimed in claims 1 or 2 wherein in step c) the pre-stored relationship correlates time-to-glitch or opening delay with the reductant supply pressure to the injector.

4. A method as claimed in claims 1 to 3 wherein said reductant is urea.

5. A method as claimed in claims 1 to 4 including additionally determining one or more parameters of injector supply voltage and determining the reductant pressure based on this parameter additionally.

6. A method as claimed in claims 1 to 5 including determining/estimating the electrical resistance of the injector and determining the reductant pressure based on this parameter additionally.

7. A method as claimed in claim 6 wherein said resistance is determined from determining supply voltage and measured current.

8. A method as claimed in any preceding claim which is performed at a reductant supply pressure substantially close to zero.