Fault tolerant oxygen control of a diesel engine air system

Transcription

1 Fault toleant oxygen contol of a diesel engine ai system Raine Nitsche, Matthias Bitze, Mahmoud El Khaldi, Géad Bloch To cite this vesion: Raine Nitsche, Matthias Bitze, Mahmoud El Khaldi, Géad Bloch. Fault toleant oxygen contol of a diesel engine ai system. IC Symposium Advances in Automotive Contol, AAC 21, Jul 21, Munich, Gemany. pp.cdrom, 21. <hal > HAL Id: hal Submitted on 21 Ap 21 HAL is a multi-disciplinay open access achive fo the deposit and dissemination of scientific eseach documents, whethe they ae published o not. The documents may come fom teaching and eseach institutions in Fance o aboad, o fom public o pivate eseach centes. L achive ouvete pluidisciplinaie HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau echeche, publiés ou non, émanant des établissements d enseignement et de echeche fançais ou étanges, des laboatoies publics ou pivés.

2 Fault Toleant Oxygen Contol of a Diesel Engine Ai System Raine Nitsche Matthias Bitze Mahmoud El Khaldi Géad Bloch Robet Bosch GmbH, Dept. CR/AEH3 Contol Theoy Goup, P.O. Box 3 2 4, D Stuttgat, Gemany ( {aine.nitsche,matthias.bitze2}@de.bosch.com) Univesité Heni Poincaé, Nancy 1, Cente de Recheche en Automatique de Nancy (CRAN), CNRS UMR 739, Nancy, Fance ( gead.bloch@esstin.uhp-nancy.f) Abstact: This pape is devoted to the fault toleant contol poblem of a Diesel engine ai system having a jammed Exhaust Gas Reciculation () valve. The fault toleant contol is based on eplaning the tajectoy in ode to tack a new contolled vaiable which is the oxygen concentation in the intake manifold instead of the fesh ai mass flow. The tajectoy planning is based on an invese model appoach, utilizing the fundamental themodynamic elations of the ai system. Keywods: Fault toleant contol, Diesel engine, Ai system, Model-based tajectoy planning 1. INTRODUCTION Diesel engines have made significant pogess in tems of pefomance ove the last yeas and have become vey popula and inceasingly attactive fo passenge cas thanks to thei low fuel consumption and high toque at low speed. Howeve, they ae significant contibutos to oveall emissions, especially of nitogen oxides (NO x ) and paticulate matte (PM, also called soot). The ai system of a Diesel engine, shown in Figue 1, is esponsible fo intoducing ai into the engine cylindes in ode to ensue the fuel combustion. The functioning of the ai system is the following. Fesh ai enteing the ai system is compessed by the compesso unit of the tubochage. The ai leaves the compesso with highe pessue, and its tempeatue inceases as a esult of the compession. A chage ai coole (CAC), not epesented in the Figue, cools down the compessed ai befoe it eaches the thottle valve (TVA; o thottle blade, TB). The fesh ai is then mixed with eciculated exhaust gas in the intake manifold and the mixtue goes into the engine 1. The waste of the combustion is then expelled fom the engine, and a pat of the exhaust gas is sent to the intake manifold ove the exhaust gas eciculation () valve to be mixed with fesh ai. The est of the exhaust gas passes though the vaiable nozzle tubine (VNT) unit of the tubochage, whee its enegy is used to dive the compesso wheel via the shaft, which connects the tubine and the compesso wheels. The main pupose of the exhaust gas eciculation is to educe the nitogen oxide (NO x ) emissions. Indeed, mixing the exhaust gas with the fesh ai educes the oxygen concentation in the intake manifold. Thus, since thee is 1 In this pape, the tem engine stands fo the combustion chambe (cylindes) and not fo the oveall engine. Figue 1. Ai system of the Diesel engine. less oxygen to eact with the fuel in the engine, fewe NO x ae poduced duing the combustion. On the othe hand, a lowe oxygen ate in the engine leads to an incomplete combustion, and induces the poduction of moe cabon hybid and paticulate matte (PM). The valve is the main component in the exhaust gas eciculation system. The valve is located between the intake and exhaust manifolds, then a pat of the exhaust gas can flow back into the engine. The ate of exhaust gas mixed with the fesh ai in the intake manifold is contolled by acting on the coss section aea of the valve. Howeve, as any physical system, valves ae subject to faults. The main fault that can affect an valve is the blocking at a cetain position, which inceases the emissions of pollutants. The pape will deal thus with the fault toleant contol (FTC) of the Diesel engine ai system having a jammed valve, with the aim of educing pollutant emissions. Section 2 intoduces the oveall faultless contol and fault toleant contol stuctues of the ai system. The diffeent

3 pats of the fault toleant contol ae descibed in Sections 3, 4 and 5. Some simulations esults ae pesented in Section 6, befoe concluding emaks. 2. AIR SYSTEM CONTROL STRUCTURE 2.1 System models and faultless contol stuctue The ai system is contolled by using a paticula modelbased appoach. Such an appoach pefoms thee tasks: planning of tajectoies with bounding conditions, calculation of nominal contol vaiables though the inveted system and stabilization of the system aound the desied tajectoy by closed-loop contol. The advantages include the consideation of physical coupling and effects, the simultaneous contol of desied values and the fulfillment of high dynamic equiements. A schematic epesentation of the ai system is pesented in Figue 2 with the main descibing vaiables. patm, Tatm HFM patm, Tatm ṁhfm m4, p4, T4 patm, Tatm ṁv NT compesso VNT ω p21, T2 CAC m21, p21, T21 TVA ṁ ṁtv A (also noted ṁ) m3, p3, T3 p3, T m22, p22, T22 ṁ out eng coole ṁeng Figue 2. Schematic epesentation of the ai path. ṁfuel engine This system is modelled with the so-called Robet Bosch Standad Simulation Libay (RBSL). The esulting ai system RBSL model consists of fou volumes connected by algebaic elations and has eleven states: - the boost pessue p 21, - the ai mass in the boost pessue volume m 21, - the intake manifold pessue p 22, - the ai mass in the intake manifold m 22, - the mass of oxygen in the intake manifold m O2,22, - the ate of fesh ai in the intake manifold,22, - the exhaust manifold pessue p 3, - the ai mass in the exhaust manifold m 3, - the downsteam pessue of the tubine (VNT) p 4, - the downsteam gas mass of the VNT m 4, - the angula speed of the tubochage ω. The manipulated vaiables, i.e. the contol inputs, ae: - the effective aea of the thottle valve (TVA) A eff - the effective aea of the valve A eff, - the effective aea of the VNT A eff V NT, TV A, and the contolled vaiables: - the fesh ai () mass flow ṁ, - the ate of gas in the intake manifold,22, - the boost pessue p 21. The model-based contol achitectue of the ai-path is shown in Figue 3. It consists of thee modules: neng The Ai System Model (ASMod) estimates the ai system signals that cannot be measued with the available sensos. Fom the modelling of the system, it also dynamically coects the measued signals, when the measued value is in the ange of low sensitivity of the senso. The outputs of the ASMod ae used by the model-based contolles, biefly descibed next. The Model-based Boost Contol (MBC) contols the boost pessue p 21 by manipulating the VNT input A eff V NT. The two-degee of feedom design is based on an invese model of the tubochage fo the feedfowad pat of the contolle and a PIstuctue fo the feedback pat. The MBC uses a family of PID contolles, each of them poviding a satisfactoy contol fo a paticula opeating point (gain scheduling). It can wok eithe in open o closed loop, depending on the opeating point. In closed loop mode, the MBC egulates the boost pessue to avoid getting too high pessue that may damage the tubochage. The Model-based Chage Contol (MCC) contols the fesh ai mass flow ṁ and/o the ate, depending on the opeating point, by acting on the thottle and valves. Again, a two-degee of feedom design is used. The MCC contains Kalman filtes which estimate the cuent aeas of the thottle and valves, an invese model of the intake manifold to calculate the desied aeas, and PI-contolles. ASMod MCC MBC TVA VNT Figue 3. Cuent ai system contol unit. 2.2 Fault toleant contol stuctue Ai system Measued signals The fault-toleant contol stategy aims at keeping this contol stuctue in the faulty case, and not designing new contolles. As the consideed fault is an actuato fault ( valve jam), thee is no possibility to adapt the contolle by simply changing its paametes fo the faulty case. Instead, altenative actuatos which have simila inteactions with the system have to be used (Blanke et al., 26). The altenative actuato used hee is the thottle valve, which is contolled by the MCC. Fo the faulty case, it is futhemoe desied to switch to a new contolled vaiable which is the oxygen concentation in the intake manifold, because this vaiable is diectly linked with the pollutants emissions. The esulting closed loop stuctue is depicted in Figue 4 with efeences to the main coesponding equations. The fist block, detailed in Section 3, calculates the desied oxygen concentation in the intake manifold O d. In 2, ode to tack this setpoint, the second task, detailed in Section 4, calculates, by invesion of the intake manifold model, the fesh ai mass flow ṁ d. A eachability analysis (Section 5) allows the MCC to eceive as input. ṁ d,final

4 m d p d 2 A Estimation Jam Position (not teated hee) ζ(t) ξ(t) λ min Oxygen Invese Reachability Concenta- tion Manifold Tables and O d 2,22 ṁ Intake d Look Up (3) (16) (2) ṁ d,final Diagnosis (not teated hee) Contol MBC, MCC, ASMod Fig. 3, TV Ai System RBSL-Plant VNT Fig. 1, Fig. 2 Figue 4. Oveall closed-loop stuctue of the poposed fault toleant contol. The known time vaiant paametes equied fo (3) and (16) ae collected in the vectos ζ(t) and ξ(t). Note that the diagnosis task and the estimation of the jam positition (Scheu, 28) ae not teated in this pape. Theefoe, this jam position is assumed hee to be pefectly known. 3. NEW CONTROLLED VARIABLE The new contolled vaiable, i.e., the oxygen concentation O2,22 in the intake manifold, is the atio of the oxygen mass flow ṁ O2,eng ove the total gas mass flow ṁ eng, going in the engine: O2,22 = ṁo 2,eng ṁ eng, (1) o, as the gas enteing the engine is exclusively composed of fesh ai and gas: O2,22 = ṁ O2, + ṁ O2, ṁ + ṁ, (2) whee O2, and O2, ae the oxygen atios in the fesh ai and gas, espectively. This gives the desied oxygen concentation in the intake manifold: O d 2,22 = ṁd O 2, + ṁ d d O 2, ṁ d +, (3) ṁd whee ṁ d is the desied fesh ai mass flow (given by the Electonic Contol Unit, ECU), and ṁ d is the desied mass flow and O d 2, the desied oxygen atio in the gas, which can be calculated in the following way. The enthalpy balance in the intake manifold can be witten as c p,mix ṁ 22 T 22 = c p, ṁ d T + c p, ṁ d T 21, (4) whee c p,mix, c p, and c p, ae the heating capacities of the mixtue ( gas + fesh ai), gas and fesh ai, espectively, T 22 is the intake manifold tempeatue, T the gas tempeatue, and T 21 the tempeatue of the fesh ai ove the thottle valve. Assuming that the upsteam pessue p 21 of the thottle valve is the same as the pessue p 22 in the intake manifold (Scheu, 28), the ideal gas law gives: ṁ 22 T 22 = p 22 V eng R Mix = pd 21 V eng R Mix, (5) whee V eng is the vaiation of the engine volume, and R Mix is the gas constant of the mixtue ( gas + fesh ai). Theefoe, the desied mass flow ṁ d needed to compute (3) can be estimated fom (4) and (5) by ˆṁ d = c p,mix p d V 21 eng R Mix c p, ṁ d T 21. (6) c p, T Moeove, with the oveall mass balance and the oxygen mass balance in the engine, the desied oxygen atio O d 2, in the gas, also needed to compute (3), can be obtained by: O d ṁ d 2, = stoic ṁ fuel O2, ṁ d + ṁ, (7) fuel whee stoic is the stoichiometic ai to fuel coefficient and ṁ fuel is the amount of injected fuel into the engine. 4. MODEL-BASED TRAJECTORY PLANNING OF THE DESIRED FRESH AIR MASS FLOW Accoding to Figue 4, the desied oxygen concentation in the intake manifold can now be used to calculate the new desied fesh ai mass flow ṁ d in the faulty case. In othe wods, a new tajectoy fo the desied fesh ai mass flow has to be planned, depending on the known jam-position of the valve and the desied oxygen concentation in the intake manifold. Fo this, a model-based appoach is used, whee the invesion of the intake manifold model is based on a flatness analysis in the sense of Fliess et al. (1992) and Rothfuß et al. (1997). 4.1 Invesion of the intake manifold model Fo a model-based tajectoy planning, the dynamics of the intake manifold can be descibed with the following state, contol input, and output definition: x = [m O2,22, m O2,22 ]T, u = ṁ, y = O2,22, (8) whee m O2,22 and m O2,22 ae espectively the masses of oxygen and all othe gases in the intake manifold, with the extenal time-vaying paametes q = [ṁ, ṁ eng, O2,, O2,, n eng ] T, (9) with n eng the engine speed. State Equations. The fist state equation is obtained by consideing the mass flow balance in the intake manifold: ṁ O2,22 = ṁ O2, + ṁ O2, ṁ O2,eng, which leads to ṁ O2,22 = ṁ O2, + ṁ O2, ṁ eng O2,22,

5 and finally to ẋ 1 = q 1 q 4 + u q 3 y q 2. (1) The second state equation is obtained as follows: ṁ = ṁ O2,22 22 ṁ O2,22 = ṁ + ṁ ṁ eng ẋ 1, leading to o Output Equation. which gives ẋ 2 = q 1 + u q 2 ẋ 1, (11) ẋ 2 = q 1 + u q 2 (q 1 q 4 + u q 3 y q 2 ). The system output y is equal to m O2,22 y = O2,22 =, m O2,22 + m O2,22 y = x 1 x 1 + x 2. (12) System Invesion. The input u can be expessed as a function of the output y and its successive deivatives. Indeed, (12) gives x 1 = y(x 1 + x 2 ) = y m 22. V As m 22 = 22 R Mix f(n eng)ṁeng, whee the known function V 22 R Mix f(n, with V eng) 22 the intake manifold volume, consides the amount of ai consumption fo the engine, the fist state becomes x 1 = Moeove, (12) gives V 22 R Mix f(n eng ) q 2 y. (13) x 2 = x 1 y x 1 and ẋ 2 = ẋ1 y ẏ x 1 y 2 ẋ 1. (14) Identifying (14) with (11) leads to q 1 + u q 2 = ẋ1 y ẏ x 1 y 2. Then, using (1) and (13), simple calculations give finally the output u as u = q V 1(q 4 y) 22 R Mix f(n q eng) 2 ẏ. (15) y q 3 New desied fesh ai mass flow. This leads diectly to the expession of the fesh ai mass flow: ṁ d = ( O 2, d O 2,22 )ṁ d O 2,22 O 2, R Mix f(n ṙ d eng)ṁeng O 2,22 O d. (16) 2,22 O 2, To compute (16), one needs to calculate the mass flow ṁ, the oxygen concentation O2, in the gas and the mass flow ṁ eng going into the engine. 4.2 mass flow To calculate the mass flow ove the jammed valve, the oifice equation can be used: ṁ = p 3 A 2Π 1 (1 Π 1 ) Tcoole,out R, (17) V 22 whee Π = p 3 p 22, T coole,out = T 3 η HE (T 3 T coolingfluid ), and A is the effective aea of the valve estimated by a Kalman filte of a diagnosis algoithm developed by Scheu (28). 4.3 Calculation of the engine mass flow To estimate the engine mass flow ṁ eng, the following equation can be used: ṁ eng = pmeas 22 V eng T22 ASMod R 2 ψ (n eng), (18) whee p meas 22 is the measued intake manifold pessue, T22 ASMod is the ASMod estimation of the intake manifold tempeatue, p meas 22 is the measued intake manifold pessue, T22 ASMod is the ASMod estimation of the intake manifold tempeatue, V eng is the engine volume, ψ (n eng ) is a coection tem epesenting the engine volumetic efficiency, R is the pefect gases constant, and c p the heating capacity of the intake gas at constant pessue is the measued intake manifold pessue. 4.4 Calculation of the oxygen ate in the exhaust gas To estimate the oxygen ate O2, in the exhaust gas, (7) can be used by eplacing the desied values by the eal values: with stoic = O2, = O2, ṁ meas ṁ meas stoic ṁ fuel + ṁ, (19) fuel 4.5 Test of the model-based tajectoy planning in the faultless case Equation (16) has been implemented in the simulation envionment and tested using a special test cycle in the faultless case. Since the faultless case is consideed, the old (given by the ECU) and the fesh ai mass flow should be equal. Figue 5 daws a compaison of these two signals, which ae shown most of the time equal. Theefoe, it can be assessed that the model-based tajectoy planning of the desied fesh ai mass flow is coect old desied Figue 5. Old ṁ d and new ṁd flows, in the faultless case. desied fesh ai mass

6 5. REACHABILITY ANALYSIS OF THE DESIRED FRESH AIR MASS FLOW AND CLOSED-LOOP STRUCTURE The next step (see Figue 4) is to check if the values of the calculated fesh ai mass flow ṁ d (16) ae physically eachable (highe limit), and not below a cetain limit (lowe limit). This eachability analysis is decibed below. Highe limit. The fesh ai mass flow depends on seveal vaiables: engine speed, injected fuel quantity, valve position, tubochage VNT position, TVA position. Howeve, it is obvious that the thottle valve (TVA) has to be fully opened to each a maximal value. Theefoe, a look-up table is ceated with only these 4 fist vaiables as inputs, and the maximal eachable fesh ai mass flow as output. The output values of this table ae the fesh ai mass flow values obtained in the faultless case fom appopiate simulation uns, whee the engine speed vaies between 15pm and 4pm with a step of 25; the injected fuel quantity vaies between 1mg/hub and 55mg/hub with a step of 5; the valve position vaies between % (fully opened) and 1% (fully closed) with a step of 1; the VNT position vaies between % and 1% with a step of 2. Lowe limit. The lowe limit of the fesh ai mass flow is govened by the ai to fuel atio λ which has to be geate than a cetain limit λ min : ṁ λ = λ min = 1.3, (2) stoic ṁ fuel whee stoic = 14.5 is the stoichiometic ai/fuel atio. Figue 6 shows an example of the desied fesh ai mass flow in the faultless case, with the maximal eachable and minimal allowed values h ige hlimit lowe limit Figue 6. The fesh ai mass flow ṁ d, with the maximal eachable and minimal allowed values. 6. APPLICATION TO DIFFERENT JAM POSITIONS Seveal simulation esults ae given hee to illustate the behavio of the poposed fault toleant contol. Faulty case 25%. When the valve is blocked at 25% position (widely opened), the fist plot in Figue 7 shows O2,22 [ ] highe limit lowe limit faulty case 25% desied measued (with FTC) measued (without FTC).12 Figue 7. Faulty case 25% at t = 5s. Fist plot: new desied fesh ai mass flow with the maximal and minimal eachable values. Second plot: oxygen concentations in the intake manifold, desied and measued (with and without FTC tajectoy planning). that the system would equie much moe fesh ai (blue line) than the physical limit (geen line) in ode to each the desied oxygen concentation in the intake manifold. A close look at the second plot, which compaes the measued oxygen concentations in the intake manifold, shows that, most of the time, the contol with model-based tajectoy planning of the desied fesh ai mass flow gives simila esults than without it, except on the low opeating points whee the FTC is able to each the desied oxygen concentation in the intake manifold. Faulty case 5%. As in the pevious case, the system needs sometimes moe fesh ai than the maximal physically eachable value in ode to each the desied oxygen concentation in the intake manifold (Figue 8, fist plot). Howeve, in spite of the physical limitation of the system, the model-based tajectoy planning of the desied fesh ai mass flow makes the system each the desied oxygen concentation in the intake manifold in the most opeating egions (Figue 8, second plot), except in the full-load egions whee the desied oxygen concentation equies to have only fesh ai in the intake manifold, and that is not possible when the valve is blocked at a middle position. Faulty case 75%. In this case, the valve is blocked at 75% position, which means almost closed. Thus, less gas comes into the intake manifold and the system needs less fesh ai to each the desied oxygen concentation in the intake manifold. Howeve, the system is blocked by the λ min -limit (2) and theefoe it is constained to have moe fesh ai than desied in the intake manifold (Figue 9, fist plot). As a consequence, the measued

7 O2,22 [ ] highe limit lowe limit faulty case 5 % desied measued (with FTC) measued (without FTC).12 Figue 8. Faulty case 5% at t = 5s. Fist plot: new desied fesh ai mass flow with the maximal and minimal eachable values. Second plot: oxygen concentations in the intake manifold, desied and measued (with and without FTC tajectoy planning) highe limit lowe limit faulty case 7 5 % oxygen concentation in the intake manifold with FTC is geate than the desied one; howeve, it is lowe than without FTC (Figue 9, second plot). 7. CONCLUSION The model-based tajectoy planning of the desied fesh ai mass flow has shown many advantages. It allows to keep the same contol stuctue, which aleady woks petty well in the faultless case. Futhemoe, egading the simulation esults fo diffeent jam positions of the valve, it has come out that this fault-toleant contol appoach gives satisfactoy esults. Indeed, it makes the system to get close to the desied oxygen concentation in the intake manifold than without any eplanning of the fesh ai mass flow tajectoy. Anothe additional actuato could be used in paallel to the thottle valve to impove the FTC pefomances. Indeed, the Vaiable Nozzle Tubine influences the boost pessue and theefoe the oxygen concentation in the intake manifold. This would equie a tajectoy planning of the desied boost pessue (El Khaldi, 29), in an analogous way of the eplanning of the desied fesh ai mass flow. REFERENCES Blanke, M., Kinnaet, M., Lunze, J., and Staoswiecki, M. (26). Diagnosis and Fault-Toleant Contol. Spinge- Velag, Belin. El Khaldi, M. (29). Fault-Toleant Contol of the Diesel Engine Ai system. Maste s thesis, Univesité Heni Poincaé Nancy 1, Robet Bosch GmbH, Dept. CR/AEH3. Fliess, M., Lévine, J., Matin, P., and Rouchon, P. (1992). On diffeentially flat nonlinea systems. In Poc. IC Symposium NOLCOS 92, Bodeaux, pp Rothfuß, R., Rudolph, J., and Zeitz, M. (1997). Flachheit: Ein neue Zugang zu Steueung und Regelung nichtlineae Systeme. Automatisieungstechnik, 45(11), Scheu, H. (28). Fehletoleante Fischluftmassenegelung eines PKW-Diesel-Motos. Maste s thesis, Univesität Stuttgat, Robet Bosch GmbH, Dept. CR/AEH O2,22 [ ] desied measued (with FTC) measued (without FTC).12 Figue 9. Faulty case 75% at t = 5s. Fist plot: new desied fesh ai mass flow with the maximal and minimal eachable values. Second plot: oxygen concentations in the intake manifold, desied and measued (with and without FTC tajectoy planning).