EP0948739A1

EP0948739A1 - Process for calculating the torque of an electronic injection internal combustion engine

Info

Publication number: EP0948739A1
Application number: EP97951317A
Authority: EP
Inventors: Eric Marcheguet; Xavier Moine
Original assignee: Renault SAS
Current assignee: Renault SAS
Priority date: 1996-12-27
Filing date: 1997-12-12
Publication date: 1999-10-13
Also published as: WO1998029718A1; US6389363B1; AU5489098A; JP2001511888A; FR2757945B1; FR2757945A1

Abstract

The invention relates to a process for calculating the torque of an internal combustion engine with electronic injection and comprising a cogged target with an indexation reference, rotating before a fixed sensor. The process consists in correcting the defects of the target by distinguishing the combustion intervals (Ti) of the target from the reference, and assigning to each interval a term ( DOLLAR g(b)i), determined in the absence of combustion from the measurement of the engine torque (Ci), which is proportional to the pressure (Pcoll) in the commutator according to the following relation: Ci = K.Pcoll = alpha ( SIGMA N + DOLLAR g(b)i)N<2> where N represents the engine power, K is a proportionality factor, and alpha is a constant term. The calculation of the engine torque (Cgi), which takes place at each combustion, is based on the term ( DOLLAR g(b)i), obtained according to the equation: Cgi = alpha ( SIGMA N + DOLLAR g(b)i)N<2>

Description

METHOD FOR CALCULATING THE TORQUE OF AN ELECTRONICALLY CONTROLLED INJECTION HEAT ENGINE

The invention relates to a method for calculating the torque of a four-stroke internal combustion engine with electronically controlled injection, in particular mounted in a motor vehicle.

More precisely, the torque measured is the average gas torque produced by the combustion of the air-petrol mixture in the different cylinders. It is interesting to measure the torque with precision over a large number of combustions to optimize certain engine settings, in particular thanks to the electronic injection computer and to diagnose certain malfunctions, including misfire or "misfire". A misfire in a cylinder of a controlled injection engine can be due to a lack of spark, a bad dosage of fuel, or a bad compression for example. This recognition of bad combustion is required by European EOBD (European On Board Diagnostic) or international OBD II (On Board Diagnostic) regulations concerning on-board diagnostic systems in vehicles, for the control of exhaust system emissions with a view to compliance with anti-pollution standards.

The method of measuring such a torque uses a device comprising a target in the form of a crown, integral with the flywheel of the engine or the crankshaft and provided with markers on its circumference, teeth for example, running past a fixed sensor. The instantaneous value of the period of movement of the teeth in front of the sensor corresponds to the measurement of the instantaneous power produced in each of the cylinders of the engine successively. Electronic calculation means use the signal delivered by the sensor to calculate the average gas torque C produced by each combustion of the gas mixture in each of the engine cylinders.

In the particular case of a four-cylinder four-stroke petrol engine operating according to the Beau de Rochas cycle, each of the four cycle times - intake, compression, combustion-expansion, exhaust - occurs during a particular U-turn of the flywheel integral with the engine crankshaft. The kinetic energy acquired by the system concerned, namely the crankshaft and the flywheel with alternative masses, is the result of the different instantaneous negative and positive torques exerted on it during each of the different times of the engine operating cycle. The gas torque Cg is calculated at each half-turn. This torque is generated during these compression and combustion-expansion phases of the gas mixtures respectively trapped in two contiguous combustion cylinders (1 and 4, 2 and 3). The other two cylinders are then in the intake and exhaust phases. Since the compression phases are less subject to variations or dispersions than the combustion-expansion phases, it is considered that the gas torque C calculated on a half-turn is relative to the cylinder in combustion and therefore that it is an estimate of the average gas torque on the two phases, compression and combustion-expansion, of the same cylinder thus trapping the same gas mixture. For example, the target has, on its periphery, 57 identical teeth regularly spaced and each formed by a niche and a hollow, and a reference tooth, of greater width equivalent to three other teeth, serving as the origin of 'indexing to allow numbering of said teeth. For a four-stroke, four-cylinder engine, the angular period T of the combustions concerns 30 teeth and is equal to half the period of rotation of the crankshaft. For a four-stroke, six-cylinder engine, the angular period of combustion T only concerns 20 teeth, etc.

The fixed sensor can be of variable reluctance, adapted to deliver an alternating signal of frequency proportional to the speed of movement of the teeth of the crown, that is to say proportional to the instantaneous speed of the flywheel.

A current method for calculating the average gas torque is described in the French patent application filed under the number 95 06780, in the name of the applicant, consisting of: - producing a primary numerical value d ^ representative of the instantaneous duration of scrolling before the sensor of each of the target teeth,

- develop from these digital values d ^, a first secondary digital value T representative of the total duration of travel in front of the sensor of each series of n teeth defining the angular interval of combustions in the engine,

- develop a second secondary numerical value Σ, representative of the projection, on the line of phase reference of the teeth corresponding to the origin of the angular periods of combustion, of the amplitude of the alternating component of the instantaneous durations d ^ of movement of the teeth in front of the sensor at the frequency of combustion in the engine, this value Σ being by example defined by the relation:

(n-1) Σ = Σ d _j _.cos (i.2π / n) 0

- elaborate the numerical value sought C from the following relation (E):

(E): C ≈ a (Σ / T ³ + β / T ² ) valid over an interval T, whatever the engine speed, a and β being two constants determined experimentally.

The term α is a constant term proportional to the rotary inertia of the motor and β is a term which is a function of the moment of inertia of the alternating masses.

The irregularities in the position of the marks on the crown will, as a first approximation, disturb the value of the term β / T ² .

In order for the measurement of the average gas torque to be reliable and usable, in particular in strategies for detecting poor combustion of an engine, developed by the injection computer, it is essential to be free from target faults, such as irregularities position markers, which can induce the risk of false detections of unacceptable bad combustion, these risks increasing with the regime. This is why the invention aims to learn and correct the defects of the target, as well as adapting to dispersions and wear of the motors.

For this, the object of the invention is a method of calculating the torque of an internal combustion engine, with injection controlled by an electronic computer, the engine being such as a target, for example in the form of a toothed ring. , provided with an indexing reference, is integral with the crankshaft and rotates in front of a tooth deflection sensor, fixedly mounted in the vicinity of the target delivering a signal to electronic means for calculating the torque, consisting, from digital values d ^ representative of the instantaneous running time in front of the sensor of each of the teeth, to develop a numerical value Σ representative of the projection, on the phase reference line of the teeth corresponding to the origin of the angular periods of the combustions, from l amplitude of the alternating component of instantaneous durations d; at the frequency of combustion in the engine, characterized in that it consists in correcting the defects of the target by the following steps:

differentiation of the angular intervals of the combustions T of the target with respect to the reference, i being an integer (equal to 1 or 2 for a four cylinder);

- assignment of a term β _ for each of the interval intervals T ^; - Recognition of the torque conditions corresponding to non-combustion such as for example a cut of fuel injection in the cylinders;

- learning the term β - in said non-combustion conditions by measuring the engine torque C ^ which is proportional to the pressure ^p _C oll in the intake manifold according to the relation: Ci = KP _coll = (ΣN + β ^ K ²

- calculation of the engine torque C • supplied to each combustion, corresponding to each interval T- of the target, from the term β ^, obtained according to the equation: C _gi = α (ΣN + β _t ) K ² N being the engine speed and K a proportionality coefficient.

Other characteristics and advantages of the invention will appear on reading the description of a particular embodiment, illustrated by the following figures which are:

- Figure 1: a front view of a toothed target, mounted on the flywheel of an internal combustion engine;

- Figure 2: the variation curves of the average measured gas torque C as a function of the manifold pressure P _co ιi 'for three different engine speed values N;

- Figure 3: a flow diagram of the different steps of the method of calculating the engine torque according to the invention.

The invention, applied to a four-stroke four-cylinder internal combustion engine, consists in learning the faults of each half-turn of the toothed target mounted at the end of the crankshaft, with the aim of correcting the calculation of the torque medium gas produced with each combustion. Indeed, there are significant differences in measured torques according to the U-turn target on which the calculation is made. These deviations can have several causes, such as for example the machining of the target, a front view of which constitutes FIG. 1. An imperfect machining of the target 1 causes defects in the measurements of durations of passage of each tooth 2 in front of the sensor 3, as well as a bad centering of the axis 4 of the target which no longer turns in a circle. Improper machining of the locating tooth 5 causes the electronic input stage of the torque measurement device to reflect an error in the calculation which leads to distortions of the signal. Finally, mounting the target at the end of the crankshaft can cause torsion and bending problems of the crankshaft. In all cases, the defect results in errors in the measurement of the time elapsed for a given angular displacement of the target.

It is shown that a term appears proportional to the square of the regime N, or to the square of the inverse of the period T of combustion. The calculation of the average gas torque C _σ , according to the principle of the software torque meter, which is based on the fact that the amplitude of the variations in instantaneous speed of the crankshaft is proportional to the gas torque and is estimated from the variation in duration teeth of the target, is carried out according to the equation (E) already given: (E) C _α = α (Σ / T ³ + β / T ² )

= α (ΣN + /?) N ² where T is a numerical value representative of the total running time before the sensor of each series of n teeth defining the angular interval of combustion in the engine, and where Σ is a representative value of the projection, on the phase reference line of the teeth corresponding to the origin angular periods of the combustions, the amplitude of the alternating component of the instantaneous durations d ^ of movement of the teeth in front of the sensor at the frequency of the combustions in the engine.

The correction of the mean gas torque therefore implies a correction of the previous equation at the level of the term in N ² , that is to say the learning of a term β relating to the angular segment to be learned. For a four-cylinder engine, there is combustion for each half-turn so that it is necessary to differentiate them to evaluate the error on each of them, starting from the reference tooth. One then affects each of the two half-turns T ^, i being an integer equal to 1 or 2, of a term β ^ and the calculation of the couple C _Q ^ is carried out from the term β according to equation (E) which becomes: C _gi = α (ΣN + β _± ) Η ² .

According to a fundamental characteristic of the invention, the learning of the term β ^ takes place under torque conditions corresponding to an absence of combustion, otherwise called non-combustion, in all the cylinders, such as for example during a cut-off. fuel injection by the electronic computer. This state of zero gas torque must be recognized, ensuring that none of the cylinders generate engine torque.

However, if the average gas torque is zero, the measured torque is not zero taking into account the pumping and air compression effects which operate in the cylinders under the effect of the rotation of the crankshaft. This torque measured in the absence of combustion is a function of the pressure in the intake manifold, measured by a pressure sensor, therefore learning conditions (speed, throttle leak rate, ...). It is considered that the torque measured at zero gas torque evolves linearly with the pressure in the manifold P _CO IJ_ _/ that is to say that its value is proportional to P _co τ_ _] _-

In the absence of combustion, for each of the half-turns T _j _ of the target, the measured torque C ^ is obtained by the following equation: _(El ) c _± = KP _CO11

For each half-turn, it is therefore necessary to calculate the term β -,, which is the solution of equation (E.): (£ -, _) C = KP _coll = α (ΣN + β _± ) N ² either : α (ΣN + δ _i ) N ² - K. P _coll = 0. From this term β ^ thus obtained, the engine torque C • is calculated according to the equation:

- *. = r αv f (VΣ.TNsl 4 + - β R.] M N2

- -gg ii ^<

According to a characteristic of the invention, the learning of the values of β ^ consists of a first step called rapid learning, taking place over a determined number P of successive top dead centers in non-combustion, for example at the end of production line of the vehicle on which the engine is mounted, controlled by an electronic ignition-injection computer, and of a second stage known as slow learning, during engine operation.

In order to have suitable learning as quickly as possible when using the vehicle, the first quick learning step consists in calculating the average j. of the first values of the term? _j _ (pmh), calculated from equation (E-,), on a determined number P of top dead centers, in non-combustion, a hundred for example, (pmh) being an integer between 1 and P corresponding to the serial number of top dead center initialized at the start of operation of the computer:

This step enables good learning to be carried out at the end of the production line, under stable, controlled and known operating conditions, on a roller bench for example, thanks to rapid adaptation to manufacturing dispersions. This average value ^ im 'stored in the electronic computer, is then used to calculate the torque C, from the output of the vehicle chain.

In the particular case of a motor vehicle whose electronic control computer has been changed during the life of the vehicle, rapid learning of the terms β -, and ^ always takes place on a number P of top dead centers counted in one or more phases of non-combustion of the engine.

To adapt to the aging of the vehicle, the slow learning step consists, at each non-combustion phase, whatever its duration counted in top dead center, to strongly filter each value of the term ^ (pmh) corresponding to the half -turn of order i, calculated at each top dead center of order pmh, so as not to take into account values learned under conditions not representative of the operation of the engine. For a half turn i considered of crankshaft, at top dead center of pmh order, the value 3 _jf (mh), obtained by this first order filtering, is equal to the filtered value β ^ (pmh-1) at previous top dead center of order pmh-1, to which is added a fraction of the difference between the value / î '(pmh) measured and the filtered value (pmh-1):

d8 _if (pmh) =? _if (pmh-l) + q [/ 3 _i (pmh) -? _if (pm -1)]

q being the filtering coefficient determined according to the desired response time for taking learning into account and pmh being an integer greater than P and less than or equal to D, corresponding to the end of the deceleration phase.

We use this filtered value / 3 ^ _f (D) = / 3 _j _ _f , obtained at the end of deceleration at top dead center of order D, for the calculation of the engine torque C at each top dead center of phase next engine acceleration: - for U-turn 1: C -, _ = [ΣN +? _lf ] N ²

- for U-turn 2: C _α2 = α [∑N + β _jf l N 2

According to another characteristic, slow learning takes place between two engine speed thresholds, which are calibration variables. By way of nonlimiting example, one can choose for a minimum threshold of 3000 rpm and for a maximum threshold of 3500 rpm.

Thus, at each phase of absence of combustion of the engine, whatever its duration, there occurs a slow learning phase of the terms β ^ and ₂ allowing the calculation of the engine torque which takes account of target faults. FIG. 3 groups together, in the form of a flowchart, the different steps of the method for calculating the torque of an engine according to the invention.

First of all, this process calculates the average gas torque at each top dead center, referenced by the pmh index, so that at each of them, step a, consisting in recognizing whether the engine is in phase combustion or non-combustion, by cutting fuel injection into the cylinders for example, must be performed.

If the engine is in the non-combustion phase, the learning conditions concerning for example the engine speed N or the throttle leakage flow rate must be fulfilled (step b) for the calculation of the terms β ^ and? ₂ , for each of the two half-turns, is carried out (step c) from the value of the pressure in the intake manifold P _coιτ • The terms β-, and? 2 thus calculated are then memorized during a step d. Then, we look at the serial number of the top dead center pmh considered and we compare it to a minimum threshold P necessary to take into account the values of β -, and 3 ₂ stored (step e). As soon as the serial number pmh of the top dead center is equal to P, a so-called fast learning step f is authorized during which the average of each of the terms β is calculated, and ₂ over the number P of dead centers high taken into account since the beginning of the process. This mean value of the terms β -, and 3 ₂ will be used to calculate the engine torque during the following top dead centers, during the engine acceleration phases.

Thus, at the next top dead center for which a combustion is recognized (step a), it is checked whether the rapid learning of the terms / 3 ₁ and β ₂ has already been carried out (step g), in which case the calculation of the gas torque means C • is made from the two appropriate terms ^ l ^e * "^ 2m ^corres P ^is ing the two half-turns (step h), to be then operated in an engine control strategy, for example (step i).

During step e, if the serial number of the top dead center pmh considered is less than the threshold P (step j), the terms β ^ and ₂ calculated in step c are not taken into account for the calculation engine torque as long as pmh is not equal to P, whether the vehicle is at the end of the production chain with a first electronic computer or it is in the service life with a new computer. On the other hand, if the serial number of the top dead center pmh considered is greater than the threshold P, rapid learning having necessarily taken place before, a step k called slow learning consists in filtering the terms /? ₁ and ₂ , calculated in step c, to deliver the filtered values β ₁ ^ () and ₂ f () at top dead center pmh = n. The filtered value β ^ (O) = β ^^, obtained at the end of deceleration at top dead center of order pmh = D, is used to calculate the engine torque C at each top dead center of the next engine acceleration phase .

This method of calculating the torque of a heat engine, correcting the defects of the target, can be advantageously used in all engine control strategies based on the analysis of the torque, such as the diagnosis of bad combustion or the recognition of the order of appearance of combustion in the different cylinders for the optimization of the controlled electronic injection. Obviously, this calculation method which has just been described in the context of a four-cylinder engine is applicable to any engine regardless of the number of cylinders, the work period is no longer then the U-turn but the interval during which combustion takes place.

Claims

1. Method for calculating the torque of a four-stroke internal combustion engine with electronically controlled injection, the engine being such as a target with an indexing reference, is integral with the crankshaft and moves in front a tooth scroll sensor, fixedly mounted in the vicinity of the target delivering a signal to electronic torque calculation means, consisting, from digital values (d ^) representative of the instantaneous scroll time in front of the sensor of each of the teeth, to develop a numerical value (Σ) representative of the projection, on the phase reference line of the teeth corresponding to the origin of the angular periods of the combustions, of the amplitude of the alternating component of the instantaneous durations (d) to the frequency of combustion in the engine, characterized in that it consists in correcting the defects of the target by:

- differentiation of the combustion intervals (T _j ) of the target compared to the reference; - assignment of a term (β _ \) for each of the intervals (T _j _); and at each top dead center:

- recognition of the torque conditions corresponding to an absence of combustion in the cylinders; - learning the term (jδ _j _) in said non-combustion conditions by measuring the engine torque (C ') which is proportional to the pressure ( ^p _C oll ^ in the manifold according to the relationship: ^c i ^{= κ} - ^p coiι = ^{Ω (∑N +} P " ² N being the engine speed, K a coefficient of proportionality and a constant term; - calculation of the engine torque ( ^c _α i) _ι supplied during the engine acceleration phase with each combustion corresponding to each half-turn (^), from the term (β ^) obtained, according to the equation: C _gi = (ΣN + β ^ K ²

2. Method for calculating the torque according to claim 4, characterized in that the learning of the term (β;), carried out during the non-combustion phase of the engine under determined learning conditions concerning the speed and the throttle leakage rate in particular , made of :

- a quick learning step on the first P high order dead spots (pmh), with (pmh) whole number between 1 and P initialized at the start of operation of the computer, consisting in calculating the average ( _r 3 _m ) of the first P values of [/ 3i (piti)], corresponding to the interval (T ^):

β (l) + β (2) + ... β _i CP) im =

P this mean value used to calculate the engine torque (^ _q i ^ during the next acceleration phase, followed by:

- a slow learning step carried out during engine operation at each non-combustion phase, consisting of first order filtering of each value [β pmh)] corresponding to the interval (T ^), calculated at each point high order death (pmh):

j3 _if (pmh) = / 3 _if (pmh-l) + q [3 _i (pmh) - j8 _if (pmh-1)] delivering a filtered value [_ (pmh)] as a function of the value filtered at the previous top dead center of order (pmh-1) and of a filtering coefficient (q) chosen according to the response time desired for the calculation of the torque, the final filtered value [β ^^ pmh)] obtained at the last top dead center of the non-combustion phase used to calculate the engine torque (C _σ ) during the next combustion phase.

3. Method for calculating the torque according to one of claims 1 to 2, characterized in that the slow learning of the term β ^) takes place between two engine speed thresholds, which are variations in calibration, for example the minimum threshold being 3000 rpm and the maximum threshold being 3500 rpm.

4. Method for calculating the torque according to one of claims 1 to 3, for a four-cylinder heat engine, characterized in that it consists in correcting the defects of the target by:

- differentiation of the two half-turns (T-) of the target with respect to the reference, i being an integer equal to 1 or 2;

- assignment of a term (β _ \ _) for each of the intervals (T ^); and at each top dead center:

- recognition of the torque conditions corresponding to an absence of combustion in the cylinders;

- learning the term (β _ \) in said non-combustion conditions by measuring the engine torque (C _j _) which is proportional to the pressure ( ^p _co n) in the manifold according to the relationship:

C 2 i ^{= K} - ^P coll = ^Ω < ^{ΣN +} ^ i) ^N N being the engine speed, K a proportionality coefficient and a constant term; - calculation of the engine torque ( ^c _g i) 'supplied during the engine acceleration phase for each combustion corresponding to each half-turn (T ^), from the term (/? _j _) obtained, according to the equation: C _gi = (ΣN + β ^ N ²

5. Method for calculating the torque according to claim 4, characterized in that the learning of the term (β i), carried out in the non-combustion phase of the engine under determined learning conditions concerning the speed and the leakage rate at butterfly in particular, consists of: - a quick learning step on the first P top dead centers of order (pmh), with (pmh) whole number between 1 and P initialized at the start of the operation of the computer, consisting in calculating the average (β _ι _m ) of the first P values of [^ (pmh)] in the non-combustion phase, corresponding to the U-turn (T _j _) of order i:

this average value used to calculate the engine torque (C ^) during the next combustion phase, followed by: - a slow learning step carried out during engine operation during each non-combustion phase, consisting of filtering the first order of each value [/ 3 _d _ (pmh)] corresponding to the u-turn of order i, calculated at each top dead center (pmh): / 3 _if (pmh) = j8 _if (pmh-l) + q [3 _i (pmh) - jS _if (pm -1)]

delivering a filtered value [/? _j _ (pmh)] as a function of the value filtered at the previous top dead center of order (pmh-1) and a filtering coefficient (q) chosen according to the response time desired for calculating the torque, the value final filtered [? i _f (pmh)] obtained at the last top dead center of the non-combustion phase used to calculate the engine torque ( ^c _α i) during the next combustion phase.

6. Method for calculating the torque according to one of claims 1 to 5, characterized in that the numerical value (Σ) representative of the projection, on the phase reference line of the teeth corresponding to the origin of the angular periods of the combustions, from the amplitude of the alternating component of instantaneous durations (d ^) to the frequency of combustions in the engine, is for example defined by the relation:

(n-1) Σ = Σ d _j _. cos (i.2π / n) 0