Patent Application
20140373508
The invention relates to a reductant delivery unit (RDU) that supplies reducing agent to an engine exhaust system and, more particularly, to an RDU that improves on the overall electrical loading over a wide temperature range by triggering the transition from peak to hold based on the detection of injector opening.
The advent of a new round of stringent emissions legislation in Europe and North America is driving the implementation of new exhaust after-treatment systems, particularly for lean-burn technologies such as compression-ignition (diesel) engines, and stratified-charge spark-ignited engines (usually with direct injection) that are operating under lean and ultra-lean conditions. Lean-burn engines exhibit high levels of nitrogen oxide (NOx) emissions that are difficult to treat in oxygen-rich exhaust environments characteristic of lean-burn combustion. Exhaust after-treatment technologies are currently being developed that will treat NOx under these conditions. One of these technologies comprises a catalyst that facilitates the reactions of ammonia (NH3) with the exhaust nitrogen oxides (NOx) to produce nitrogen (N2) and water (H2O). This technology is referred to as Selective Catalytic Reduction (SCR).
Ammonia is difficult to handle in its pure form in the automotive environment. Therefore, it is customary with these systems to use a liquid aqueous urea solution, typically at a 32% concentration of urea solution (CO (NH2)2). The solution is referred to as AUS-32, and is also known under its commercial name of AdBlue. The urea solution is delivered to the hot exhaust stream and is transformed into ammonia in the exhaust after undergoing thermolysis, or thermal decomposition, into ammonia and isocyanic acid (HNCO). The isocyanic acid then undergoes a hydrolysis with the water present in the exhaust and is transformed into ammonia and carbon dioxide (CO2). The ammonia resulting from the thermolysis and the hydrolysis then undergoes a catalyzed reaction with the nitrogen oxides as described previously.
The AUS-32 injector is typically installed directly on the engine exhaust, which exposes it to a very hot environment. In order to reduce the electrical thermal loading of the injector, so-called peak-and-hold injector drivers have been implemented. With reference to
The low current level is typically at a value that is much lower than the full saturated current level of the injector, and higher than the minimum level of current needed to maintain the injector (solenoid) open. In today's driver circuits, the transition from the rise to peak to the hold phase is usually triggered by a current level detection on the current; once the current reaches that level, the subsequent hold phase is enabled.
The main advantage to operating the injector with a low hold phase is the lower electrical load that results compared to operation under saturated switch conditions. For example, an injector with a 12-ohm coil, supplied by 14V, will dissipate 16.3 Watts (I=1.2 A). An injector that is operated with a 0.5 A hold mode will dissipate 7 Watts during the hold phase.
A disadvantage arises as the temperature increases and the injector resistance increases. As the resistance increases, the time required for the current to reach a given threshold will increase due to the dependence of the time on the coil resistance. In a limiting case with a sufficiently high temperature, the current may never reach the transition threshold, and yet the injector is open. The temperature range where this would occur is dependent on the difference between the selected transition current level and the minimum current required to open the injector. This difference will be non-zero to take into account tolerances and variations of the various elements that make up the electrical and magnetic circuits.
As an example, today the peak current is specified at a level of 0.8 A. This is above the required nominal opening current of 0.6 A. The specified nominal hold current is 0.5 A. A situation could arise where the saturated injector current is 0.7 A, for example, if the available electrical supply voltage is only 12V, but the injector coil resistance is 17Ω, (e.g., the injector coil temperature is 130 C). An illustration of what the current waveform would look like in this case is shown in
Thus, there is a need for an RDU that improves on the overall electrical loading over a wide temperature range by triggering the transition from peak to hold based on the detection of injector opening.
An object of the invention is to fulfill the needs referred to above. In accordance with the principles of the present invention, this objective is obtained by a trigger circuit for a peak and hold driver circuit for a reductant delivery unit (RDU) having a solenoid-operated injector for selective catalytic reduction (SCR) after-treatment for vehicles. The peak and hold driver circuit is constructed and arranged to actuate the injector in a rise-to-peak current phase followed by a low current hold phase. The trigger circuit includes an injector open detection circuit constructed and arranged, based on a detected opening event of the injector, to trigger a transition from the rise-to-peak phase to the subsequent hold phase of the injector.
In accordance with another aspect of an embodiment, a reductant delivery unit (RDU) and control unit for selective catalytic reduction (SCR) after-treatment for vehicles includes an RDU having a solenoid-operated injector. A control unit is electrically connected with the solenoid. The control unit has a peak and hold driver circuit constructed and arranged to actuate the injector in a rise-to-peak current phase followed by a low current hold phase. The driver circuit includes an injector open detection circuit constructed and arranged, based on a detected opening event of the injector, to trigger a transition from the rise-to-peak phase to the subsequent hold phase of the injector.
In accordance with yet another aspect of an embodiment, a method of triggering a reductant delivery unit (RDU) having a solenoid-operated injector for selective catalytic reduction (SCR) after-treatment for vehicles detects an opening event of the injector, and based on the detecting, step, triggers a transition from a rise-to-peak phase to a subsequent hold phase of the injector, thereby limiting a thermal load on the injector to a minimum required to ensure opening of the injector.
Other objects, features and characteristics of the present invention, as well as the methods of operation and the functions of the related elements of the structure, the combination of parts and economics of manufacture will become more apparent upon consideration of the following detailed description and appended claims with reference to the accompanying drawings, all of which form a part of this specification.
The invention will be better understood from the following detailed description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts, in which:
The disclosed embodiment relates to a control strategy to eliminate the risk of an undesirable increase in the thermal load of an injector of an RDU at already elevated operating temperatures. The detection of injector opening and closing events by analysis of the voltage or current is well known. An example of an opening event detection by current analysis (indicated by “OPP2”) is shown in
The detection of these events is useful for diagnostics purposes, and can also be used to compensate for lifetime shifts in flow due to changes in the duration of the injector transient phase. With reference to
With reference to
With reference to
The RDU 36 includes the solenoid fluid injector 34 that provides a metering function of fluid and provides the spray preparation of the fluid into the exhaust gas flow path of a vehicle in a dosing application. The fluid injector 34 is preferably a gasoline, electrically operated, solenoid (coil) fuel injector such as the type disclosed in U.S. Pat. No. 6,685,112, the content of which is hereby incorporated by reference into this specification. Thus, when the coil of the injector 34 is energized, a valve in the injector opens, causing reductant to be delivered to an exhaust flow path in the conventional manner.
By using the injector opening event as a trigger, the thermal loading of the injector is thereby limited to the minimum required to ensure opening of the injector. The risk of a drawn-out rise-to-peak phase and therefore additional thermal loading is also avoided.
The foregoing preferred embodiments have been shown and described for the purposes of illustrating the structural and functional principles of the present invention, as well as illustrating the methods of employing the preferred embodiments and are subject to change without departing from such principles. Therefore, this invention includes all modifications encompassed within the spirit of the following claims.
