REDUCTANT DELIVERY UNIT FOR AUTOMOTIVE SELECTIVE CATALYTIC REDUCTION WITH THERMALLY OPTIMIZED PEAK-AND-HOLD ACTUATION BASED ON AN INJECTOR OPEN EVENT

Abstract

A trigger circuit is provided 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.

Description

FIELD

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.

BACKGROUND

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 FIG. 1, the function of this driver is to actuate the injector in two modes describing the injector current: a rise-to-peak current phase, followed by a low current hold phase (current control at high switching frequency).

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. FIG. 2 shows a peak-and-hold circuit 10 having a conventional peak current detection and trigger circuit 12.

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 FIG. 3. The risk of this condition is then to have an injector operating already at an elevated temperature that is subjected to an increased electrical thermal load.

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.

SUMMARY

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.

BRIEF DESCRIPTION OF THE DRAWINGS

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:

FIG. 1 is view of conventional injector current, showing rise-to-peak phase followed by a low current hold phase.

FIG. 2 is a block diagram of a conventional peak-and-hold circuit with a peak current detection and trigger circuit.

FIG. 3 is view of a conventional current waveform showing saturation current at 0.7 A.

FIG. 4 shows conventional opening event detection of an injector by current analysis.

FIG. 5 shows detection of opening time from second derivative of coil current.

FIG. 6 is a peak-and-hold circuit block diagram with an injector open detection circuit provided in accordance with an embodiment.

FIG. 7 shows a current waveform that results from the circuit of FIG. 6.

FIG. 8 is a view of a control unit containing the circuits of FIG. 6 for operating an RDU.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

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 FIG. 4, where the accelerometer signal is 14, the voltage signal is 16, the test pulse is 18, and the current signal is 20.

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 FIG. 5, one embodiment of such detection is in hardware form with a circuit that generates an electrical pulse 22 upon the opening detection using the second derivative 24 of the current waveform as an input. The spurious initial pulse 26 can be ignored by appropriate use of enable windows, e.g., only allowing the pulse through during certain pre-determined times during the injector pulse-width. An example of using the second derivative of current in detecting a state of an injector is disclosed in co-pending, U.S. Provisional Application, filed on the same date as this regular application, entitled, “Solenoid-Actuator-Armature End-of-Motion Detection, Attorney Docket Number: 2012P02238US, the contents of which is hereby incorporated by reference into this specification.

With reference to FIG. 6, a block diagram is shown of a peak-and-hold driver circuit 10′ constructed and arranged to actuate an injector in a rise-to-peak current phase followed by a low current hold phase in accordance with an embodiment. The circuit 10′ includes a trigger circuit 28 having an injector open detection circuit 29. Thus, the trigger circuit 28 replaces the prior art current threshold trigger circuit 12 of FIG. 2. The circuit 10′ uses the injector opening event, as detected, for example, by use of the second derivative 24 of the current waveform noted above, to trigger the transition from the rise-to-peak phase to the subsequent hold phase of the injector actuation control. In the embodiment, the detection circuit 29 includes a processing or differentiating circuit 31 for differentiating current. Other conventional methods of detecting an opening state of an actuator or injector can be used instead of using the second derivative of current. An illustration of the current waveform 30 that would result from implementation of the embodiment is shown in FIG. 7.

With reference to FIG. 8, the circuit 10′ including the trigger circuit 28 is preferably provided in a control unit 32 that is electrically connected to a solenoid operated injector 34 of an RDU, generally indicated at 36. The RDU 36 can be employed in a system of the type disclosed in U.S. Patent Application Publication No. 2008/0236147 A1, the contents of which is hereby incorporated by reference into this specification.

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.

Claims

1. 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 being constructed and arranged to actuate the injector in a rise-to-peak current phase followed by a low current hold phase, the trigger circuit comprising:

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.

2. The trigger circuit of claim 1, in combination with the driver circuit so that the driver circuit includes the trigger circuit.

3. The combination of claim 2, in further combination with the RDU.

4. The combination of claim 3, wherein the driver circuit and trigger circuit are part of a control unit electrically connected with the RDU.

5. The trigger circuit of claim 1, wherein the open detection circuit is constructed and arranged to trigger the transition based on an electrical pulse generated upon detecting the opening event of the injector by using a second derivative of a current waveform as an input.

6. The trigger circuit of claim 5, wherein the open detection circuit includes a differentiating circuit.

7. A reductant delivery unit (RDU) and control unit for selective catalytic reduction (SCR) after-treatment for vehicles, the RDU and control unit comprising:

an RDU having a solenoid-operated injector, and

a control unit electrically connected with the injector, the control unit having 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 including 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.

8. The RDU and control unit of claim 7, wherein the injector open detection circuit is constructed and arranged to trigger the transition based on an electrical pulse generated upon detecting the opening event of the injector by using a second derivative of a current waveform as an input

9. The RDU and control unit of claim 8, wherein the injector open detection circuit includes a differentiating circuit.

10. A method of triggering a reductant delivery unit (RDU) having a solenoid-operated injector for selective catalytic reduction (SCR) after-treatment for vehicles, the method comprising:

detecting an opening event of the injector, and

based on the detecting, step, triggering 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.

11. The method of claim 10, wherein the detecting step uses a second derivative of a current waveform of the injector.