GB2501704A

GB2501704A - Estimating a fluid mass flow injected by an injector

Info

Publication number: GB2501704A
Application number: GB1207580.0A
Authority: GB
Inventors: Giovanni David; Igor Zanetti
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2012-04-30
Filing date: 2012-04-30
Publication date: 2013-11-06
Also published as: GB201207580D0

Abstract

An embodiment of the invention provides a method of estimating a fluid mass flow injected by an injector controlled by an Electronic Control Unit managing an internal combustion engine. The injector may comprise a fuel injector or a diesel exhaust fluid injector. The method comprises the steps of - measuring an elapsed time from a starting instant, - determining an injector energizing time as a function of a requested mass of fluid value, - activating the injector for the injector energizing time for injecting the requested mass of fluid, - adding the value of the requested mass of fluid to an accumulator variable, -repeating the preceding steps until a stopping condition is verified, - reading a final value reached by the accumulator variable when the stopping condition is verified, - dividing the final value of the accumulator variable by the final value of the elapsed time to determine an estimated mass flow of fluid injected by the injector.

Description

METHOD OFESTIMAT/N3 A FLUID MASS FLOW INJECTED BYAN INJECTOR

TECHNICAL FIELD

The present disclosure relates to a method of estimating a fluid mass flow injected by an injector controlled by an Electronic Control Unit in an Internal Combustion Engine.

BACKGROUND

Internal combustion engines, in particular Diesel engines, are generally equipped with exhaust gas after-treatment systems in order to reduce pollution due to engine emissions.

In particular, among exhaust gas after-treatment systems, SCR (Selective Catalytic Reduction) devices are generally provided.

An SCR (Selective Catalytic Reduction) is a catalytic device in which the nitrogen oxides (NOr) contained in the exhaust gas are reduced into diatonic nitrogen (N2) and water (H20), with the aid of a gaseous reducing agent, typically ammonia (NH3) that can be obtained by urea (CH4N2O) thermo-hydrolysis and that is absorbed inside catalyst.

Typically, urea is injected in the exhaust line and mixed with the exhaust gas upstream the 8CR.

Other fluids can be used in a an SCR in lieu of urea and are generally referred to as Diesel Exhaust Fluids (DEF).

The SCR device is mounted in the exhaust pipe of the internal combustion engine and is associated to an injector that injects the urea solution supplied by a pump from an urea tank.

The opening of the injector is commanded by an Electronic Control Unit (ECU) of the engine foflowing known strategies that determine a target or requested DEF mass flow to be injected.

The control in closed loop of the DEF quantity injected is not easily feasible due to the high costs of an DEF mass flow sensor and due to the difficulty of inserting such sensor in an already cramped space inside the engine compartment of the vehicle.

An object of an embodiment of the invention is to create a method of estimating a DEF mass flow injected into the exhaust gas pipe of the combustion engine.

Another object is to provide a DEF mass flow estimate without using complex devices and by taking advantage from the computational capabilities of the Electronic Control Unit (ECU) of the vehicle.

Another object of the present disclosure is to meet these goals by means of a simple, rational and inexpensive solution.

These and other objects are achieved by a method for operating a fuel injection system having the features recited in the independent claim.

These objects are achieved by a method, by an engine, by a computer program and computer program product, by an apparatus and by an automotive system having the features recited in the independent claims.

The dependent claims delineate preferred and/or especially advantageous aspects.

SUMMARY

An embodiment of the disclosure provides a method of estimating a fluid mass flow injected by an injector controlled byan Electronic Control Unit managing an internal combustion engine, wherein the method comprises the steps of: -measuring an elapsed time from a starting instant, -determining an injector energizing time as a function of a requested mass of fluid value, -activating the injector for the injector energizing time for injecting the requested mass of fluid, -adding the value of the requested mass of fluid to an accumulator variable, -repeating the preceding steps until a stopping condition is verified, -reading a final value reached by the accumulator variable when the stopping condition is verified, -dividing the final value of the accumulator variable by the final value of the elapsed time to determine an estimated mass flow of fluid injected by the injector.

An advantage of this embodiment is that it allows a more accurate estimation of the DEF mass flow injected.

This estimation may be used for many functions of the control software of the vehicle, including for the catalyst state estimator, namely a known function that estimates NH3 storage.

Based on the DEF mass flow estimation, all SCR statistics variables are calculated (i.e. distance before DEF tank is empty), these are needed to act all strategies required by law (i.e. vehicle speed limitation due to short distance to empty).

The same steps of the method can be used in order to estimate the fluid mass flow injected by other injectors controlled by an ECU, such as fuel injectors.

According to an embodiment of the invention, the stopping condition is verified when the elapsed time reaches a predetermined time threshold.

This embodiment allows for an estimation of the injected DEF mass flow along a predetermined period, for example a predetermined driving cycle.

According to another embodiment of the invention, the stopping condition is verified when the accumulator variable reaches a predetermined threshold mass value.

This embodiment allows for an estimation of the injected DEF mass flow along a predetermined task such as, for example, a diagnostic task of the SCR.

According to another embodiment of the invention, after the estimated mass flow of fluid is determined, the final value is reset to zero.

This embodiment allows the calculation of new values of the estimated fluid mass flow, According to another embodiment of the invention, the injector commanded is a Diesel Exhaust Fluid injector.

According to another embodiment of the invention, the injector commanded is a fuel injector.

Still another embodiment of the invention provides an apparatus for estimating a fluid mass flow injected by an injector controlled by an Electronic Control Unit managing an internal combustion engine, wherein the apparatus comprises: -means for measuring an elapsed time from a starting instant, -means for determining an injector energizing time as a function of a requested mass of fluid value, -means for activating the injector for the injector energizing time for injecting the requested mass of fluid, -means for adding the value of the requested mass of fluid to an accumulator variable, -means for repeating the preceding steps until a stopping condition is verified, -means for reading a final value reached by the accumulator variable when the stopping condition is verified, -means for dividing the final value of the accumulator variable by the final value of the elapsed time to determine an estimated mass flow of fluid injected by the injector.

Another embodiment of the invention provides an automotive system comprising an internal combustion engine, wherein the internal combustion engine is equipped with an Electronic Control Unit connected to fluid injectors, wherein the Electronic Control Unit is configured to: -measure an elapsed time from a starting instant, -determine an injector energizing time as a function of a requested mass of fluid value, -activate the injector for the injector energizing time for injecting the requested mass of fluid, -add the value of the requested mass of fluid to an accumulator variable, -repeat the preceding steps until a stopping condition is verified, -read a final value reached by the accumulator variable when the stopping condition is verified, -divide the final value of the accumulator variable by the final value of the elapsed time to determine an estimated mass flow of fluid injected by the injector.

Both these last two embodiments have the same advantage of the method disclosed above.

The method according to one of its aspects can be carried out with the help of a computer program comprising a program-code for carrying out all the steps of the method described above, and in the form of computer program product comprising the computer program.

The computer program product can be embodied as a control apparatus for an internal combustion engine, comprising an Electronic Control Unit (ECU), a data carrier associated to the ECU, and the computer program stored in a data carrier, so that the control apparatus defines the embodiments described in the same way as the method. In this case, when the control apparatus executes the computer program all the steps of the method described above are carried out.

The method according to a further aspect can be also embodied as an electromagnetic signal, said signal being modulated to carry a sequence of data bits which represents a computer program to carry out all steps of the method.

A still further aspect of the disclosure provides an internal combustion engine specially arranged for carrying out the method claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will now be described, by way of example, with reference to the accompanying drawings, wherein like numerals denote like elements, and in which: Figure 1 shows an automotive system; Figure 2 is a cross-section of an internal combustion engine belonging to the automotive system of figure 1; Figure 3 represents schematically a portion of an aftertreatment system of the automotive system of figures 1-2, Figure 4 is a schematic representation of a control logic that can be employed in an embodiment of the method of the invention, Figure 5 is a flowchart representing an embodiment of the method of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will now be described with reference to the enclosed drawings without intent to limit application and uses.

Some embodiments may include an automotive system 100, as shown in Figures 1 and 2, that includes an internal combustion engine (ICE) 110 having an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to rotate a crankshaft 145.

A cylinder head 130 cooperates with the piston 140 to define a combustion chamber 150.

A fuel and air mixture (not shown) is disposed in the combustion chamber 150 and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 140.

The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 in fluid communication with a high pressure fuel pump 180 that increases the pressure of the fuel received from a fuel source 190.

Each of the cylinders 125 has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145. The valves 215 selectively allow air into the combustion chamber 150 from an intake port 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.

The air may be distributed to the air intake port(s) 210 through an intake manifold 200. An air intake duct 205 may provide air from the ambient environment to the intake manifold 200. In other embodiments, a throttle body 330 may be provided to regulate the flow of air into the manifold 200.

In still other embodiments, a forced air system such as a turbocharger 230, having a compressor 240 rotationally coupled to a turbine 250, may be provided. Rotation of the compressor 240 increases the pressure and temperature of the air in the duct 205 and manifold 200. An intercooler 260 disposed in the duct 205 may reduce the temperature of the air. The turbine 250 rotates by receiving exhaust gases from an exhaust manifold 225 that directs exhaust gases from the exhaust ports 220 and through a series of vanes prior to expansion through the turbine 250. The exhaust gases exit the turbine 250 and are directed into an exhaust system 270. This example shows a variable geometry turbine (VOT) with a VGT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 250. In other embodiments, the turbocharger 230 may be fixed geometry and/or include a waste gate.

The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust aftertreatment devices 280,285. The afterireatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment devices 280,285 include1 but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NQ traps, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems 285, and particulate filters.

In fig. 3 a portion of an aftertreatment system equipped with a selective catalytic reduction (8CR) system 285 is described in more detail.

Other embodiments may include an exhaust gas recirculation (EGR) system 300 coupled between the exhaust manifold 225 and the intake manifold 200.

Another EGR system (not represented for simplicity) could be coupled between the pipes after turbine and the pipe before compressor (low pressure EGR or long-route EGR).

The EGR system 300 may include an EGR cooler 310 to reduce the temperature of the exhaust gases in the EGR system 300. An EGR valve 320 regulates a flow of exhaust gases in the EGR system 300.

The automotive system 100 may further include an electronic control unit (ECU) 450 in communication with one or more sensors and/pr devices associated with the ICE 110.

The ECU 450 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE 110. The sensors include, but are not limited to, a mass airflow and temperature sensor 340, a manifold pressure and temperature sensor 350, a combustion pressure sensor 360, coolant and oil temperature and level sensors 380, a fuel rail pressure sensor 400, a cam position sensor 410, a crank position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, and an accelerator pedal position sensor 445.

According to some embodiments of the invention, the ECU 450 may receive signals from the fuel injection system 600, as will be explained hereinafter.

Furthermore, the ECU 450 may generate output signals to various control devices that are arranged to control the operation of the ICE 110, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, the VGT actuator 290, and the cam phaser 155. Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors and devices, but some are omitted for clarity.

Turning now to the ECU 450, this apparatus may include a digital central processing unit (CPU) in communication with a memory system, or data carrier 460, and an interface bus. The CPU is configured to execute instructions stored as a program in the memory system, and send and receive signals to/from the interface bus. The memory system may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices. The program may embody the methods disclosed herein, allowing the CPU to carryout out the steps of such methods and control the ICE 110.

B

In Figure 3 a selective catalytic reduction (SCR) system 285 is represented, the SCR system 285 being provided with a 8CR catalyst 287 in the exhaust pipe 275 of the exhaust system 270 of the internal combustion engine 110.

The SCR catalyst 287 can be fed with a Diesel Exhaust Fluid (DEE), for example urea1 that is stored in a DEF tank 520, in order to reduce the nitrogen oxides (NO) contained in the exhaust into diatonic nitrogen (N2) and water (H20).

The DEF is provided to a DEF injector 500 by means of a DEF pump 510 that receives the DEF from the DEF tank 520.

The DEF injector 500 can be controlled by the ECU 450 of the automotive system 100.

The ECU can calculate appropriate energizing times ET_lnj of the DEF injector 500 in order to inject a requested mass of DEF into the exhaust gas stream upstream of the SCR catalyst 287.

The exhaust pipe 275 may also be equipped with a NO sensor 503 upstream of the SCR catalyst 287 and with a NO sensor 507 downstream of the SCR catalyst 287, in order to provide data to the ECU on the operation of the SCR catalyst 287.

A schematic representation of some of the main functions of an embodiment of the method of the invention is now disclosed with reference fig. 4.

The DEE injector 500 is commanded by the ECU 450 employing a strategy (block 600) to inject a defined quantity of DEF fluid upstream of the 8CR catalyst 287.

The injector command strategy may be time synchronous or asynchronous. This means that when the injector command strategy is time synchronous, it will be performed until a predetermined time value threshold tth is reached. In this case an elapsed time from a starting instant can be measured and a stopping condition may be set in order to stop the strategy when the stopping condition is verified, namely when the elapsed time reaches the predetermined time threshold tth.

If on the contrary the injector command strategy is time asynchronous, it will be performed until a predetermined task is completed, for example until a threshold mass value DEF_massth is reached.

In any case, the injector command strategy receives a DEF mass request determined by the ECU 450 according to various engine parameters and by known methods, and calculates an energizing time ET_lnj of the DEF injector 500. Then the ECU 450 commands the opening of the injector 500 for such energizing time ET_lnj, in order to inject the required mass DEF_lnj of DEF upstream of the SCR catalyst 287.

In addition, the value DEF_lnj of the requested mass of fluid is added to an accumulator variable value DEF_Mass stored in a memory of the Electronic Control Unit 450.

The accumulator variable DEF_Mass performs the function of summing up the various values of the variable DEF_lnj in order to keep track of a value that is representative of a total injected mass value of DEF in a certain period.

This may be done by storing the various values of the accumulator variable DEF_Mass into a memory of the data carrier 460 of the Electronic Control Unit 450.

More generally, an accumulator function (block 610) calculates the following equation: DEF_Mass = Z DEF_lnj.

The determination of a final value DEF_Mass of the accumulator variable can be performed when a predetermined time threshold tth is reached. In this case the stopping condition may verified.

At this time the final value DEF_Mass of the accumulator variable is divided by a predetermined interval of time t_task to determine an estimated mass flow of fluid DEF_Flow injected by the injector.

The accumulator function may comprise two sub-functions, namely a SUM sub-function that allows to add a new DEF injected mass value to the current accumulated one as already described, and a GET sub-function that allows to read the final accumulated injected DEF mass value and, under conditions explained below, reset it to a starting value such as, for example, zero.

This embodiment of the invention provides also for a injected DEF mass flow estimation function (block 620) which is time synchronous.

This DEF mass flow estimation function calculates the DEF injected mass flow as a function of a time synchronous execution task.

For example, a task may be defined in terms of a predefined length of time by setting a time threshold value tth to end the task.

The accumulator function (block 610) is shared between the injector command strategy (block 600) and the injected DEF mass flow estimation (block 620).

The accumulator performs the SUM function every time an injection is required, adding the injected mass quantity to the previously accumulated one.

The injected DEF mass flow estimation function performs the GET sub-function reading the final accumulated mass and setting it to zero.

Any arbitration policy can be used to decide what sub-functions have to access the accumulator first, in case both sub-functions are to be performed at the same instant of time.

A flowchart representing an embodiment of the method of the invention is depicted in Figure 5.

At the start of the method, the ECU 450 generates a DEF mass request depending on various engine conditions (block 700) and according to known strategies.

The ECU 450 calculates an energizing time of the DEF injector 500 and commands the opening of the DEF injector 500 for such energizing time in order to inject the required mass of DEF fluid upstream of the SCR catalyst 287 (block 710).

The injected mass value is the added to the accumulator (block 720).

A check is then performed in order to verify if the time t elapsed from the start of the method has reached the predefined time threshold t (block 730).

If the answer is negative, the method performs another cycle by generating a new mass request, commanding the injector for the required energizing time ET_lnj and adding the DEE injected mass value into the accumulator variable DEE_Mass.

lithe answer is affirmative, the final mass value DEF_Mass is read by the ECU 450 and is divided by a predefined length of time Ltask (block 740), according to the following equation: DEF_nuzss DEFJ low = task In this case the predefined length of time task may be equal to the time elapsed until the predefined time threshold tth.

The value of DEF mass flow DEF_flow can be expressed in [g/s and can be used in any case in which an estimation of a DEF injected flow mass is required.

Finally the accumulated mass value DEF_Mass is reset (block 750). This value may be, for example, reset to zero.

According to another embodiment of the method of the invention, the addition of the values DEF_lnj of the requested mass of fluid to the accumulator variable value DEF_Mass is performed until a threshold mass value DEF_massth is reached.

In this case another stopping condition may be set in order to stop the strategy when the stopping condition is verified. The stopping condition may be verified when the accumulator variable reaches a predetermined threshold mass value DEF_massth.

In this case, the estimated injected mass value DEF_Flow is also calculated by dividing the value of the accumulated DEF variable DEF_Mass by a predefined length of time Uask.

This also allows to have an estimated injected mass value OFF_Flow that can be useful to other functions of the ECU 450 and/or to be displayed on the dashboard of the vehicle.

The invention has been explained with reference to an aftertreatment system and a DEF injector for injecting a DEF into an upstream position of an exhaust line with respect to an SCR catalyst, but the concepts involved in the various embodiments of the invention may also be applied to the estimation of a fuel quantity injected in a cylinder of the engine by a fuel injector.

In this case the estimated injected mass value DEF_Flow is representaitve of a fuel mass flow.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

REFERENCE NUMBERS

automotive system internal combustion engine (ICE) engine block 125 cylinder cylinder head camshaft piston crankshaft 150 combustion chamber cam phaser fuel injector intake manifold 205 air intake duct 210 intake airport 215 valves of the cylinder 220 exhaust gas port 225 exhaust manifold 230 turbocharger 2 0 240 compressor 244 exhaust line portion 250 turbine 260 intercooler 270 exhaust system 275 exhaust pipe 280 exhaust aftertreatment device 285 SCR system 287 SCR catalyst 290 VGT actuator 300 EGR system 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow and temperature sensor 350 manifold pressure and temperature sensor 360 combustion pressure sensor 380 coolant and oil temperature and level sensors 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure sensor 445 accelerator pedal position sensor 450 electronic control unit (ECU) 460 data carrier 500 DEF injector 503 upstream NO sensor 507 downstream NQ sensor 5lODEFpump 520 DEF tank 600 block 610 block 620 block 700 block 710 block 720 block 730 block 740 block 750 block

Claims

CLAIMS1. A method of estimating a fluid mass flow injected by an injector (160.500) controlled by an Electronic Control Unit (450) managing an internal combustion engine (110), wherein the method comprises the steps of: -measuring an elapsed time from a starting instant, -determining an injector energizing time (ET_lnj) as a function of a requested mass of fluid value (DEF_lnj), -activating the injector (160,500) for the injector energizing time (ET_lnj) for injecting the requested mass of fluid, -adding the value (DEF_lnj) of the requested mass of fluid to an accumulator variable, -repeating the preceding steps until a stopping condition is verified, -reading a final value (DEF_Mass) reached by the accumulator variable when the stopping condition is verified, -dividing the final value (DEF_Mass) of the accumulator variable by the final value (t_task) of the elapsed time to determine an estimated mass flow of fluid (DEF_Flow) injected by the injector (160,500).
2. A method according to claim 1, in which the stopping condition is verified when the elapsed time reaches a predetermined time threshold (tth).
3. A method according to claim 1, in which the stopping condition is verified when the accumulator variable reaches a predetermined threshold mass value (DEF_massh).
4. A method according to claim 1, in which after the estimated mass flow of fluid (DEF_Flow) is determined, the final value (DEF_Mass) is reset to zero.
5. A method according to claim 1, in which the injector commanded is a Diesel Exhaust Fluid injector (500).
6. A method according to claim 1, in which the injector commanded is a fuel injector (160).
7. An internal combustion engine (110), the combustion engine (110) comprising sensors for the measurement of combustion parameters, the engine (110) being equipped with a fluid injection system and an Electronic Control Unit (ECU) (450) configured for carrying out the method according to any of the preceding claims.
8. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1-6.
9. Computer program product on which the computer program according to claim 8 is stored.
10. Control apparatus for an internal combustion engine (110), comprising an Electronic Control Unit (450), a data carrier (460) associated to the Electronic Control Unit (450) and a computer program according to claim 8 stored in the data carrier (460).