FR2919678A1 - METHOD AND DEVICE FOR DIAGNOSING INJECTOR LEAKAGE IN AN INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

The present invention relates in particular to a method for diagnosing an injector leak in an injection system of an internal combustion engine fitted to a motor vehicle, provided with a number n of rollers An, this injection system comprising a number n of injectors Bnqui each send fuel to a respective cylinder Aidu motor, i being between 1 and n.Ce method comprises the following steps which consist of: a) determining a phase of absence of voluntary fuel injection in the engine, b) during this phase, and for each of the cylinders Ai, determining the corresponding average gas torque Ci representative of the contribution of this cylinder to the output torque of the engine; c) comparing the value of this pair Ci, or d a variable dependent on this torque, at a reference value; d) diagnose a state of leakage when a mathematical relationship between this torque value or this variable and the reference value is verified ed.

Description

The present invention relates to a method and a device for

  diagnosing an injector leak in an injection system of an internal combustion engine fitted to a motor vehicle. The present invention is in the field of internal combustion rotary engines (gasoline or diesel), direct or indirect fuel injection with n number of cylinders. The current injection systems have the particularity of injecting the fuel at high pressures into the combustion chamber so as to obtain a spray of this fuel facilitating combustion. Injectors are fed with fuel at high pressures. One of the biggest risks to these systems is the possibility that an injector will remain locked in the open position, which would result in a continuous supply of fuel to the chamber. The effects of continuous injection into a cylinder are excessive fuel consumption, abnormal combustions (i.e., non-phased injections) and / or combustion of excessive intensity, resulting in peaks of temperature and pressure in the chamber equipped with the defective injector. A short period of operation with an open injector delivering a large leakage rate can lead to serious damage to the engine components such as rods or pistons, which can eventually lead to engine failure. An injector leak detection method is presented in EP-A-0 785 349. This method is based on the detection of noise from combustion, detected with the aid of an accelerometer placed on the engine block. Simultaneously, a computer receives the signal from a PMH sensor ("top dead center"), the sensor placed on the cam shaft, and that from the accelerometer. The amplitude of this latter signal can be compared to the amplitude of a reference signal. If the amplitude of the measured signal is greater than the reference signal, an injector blocked in the open position is diagnosed.

  Furthermore, the angular position for which the intensity of the signal from the accelerometer exceeds a threshold, can be compared to a reference angular position at which an injector opening command is requested. If a combustion signal is detected before the activation angle of the injector, an injector blocked in the open position is diagnosed. Also disclosed in EP-A-0 785 358 is a multi-stage injector leak detection method. First, the fuel rail pressure and fuel consumption are compared to reference values.

  If the pressure is lower than the reference and the consumption exceeds the reference, then a leak is suspected. The flow injected into the cylinders is then reduced. The problem then consists in determining whether it is a leak outside the cylinder, that is to say at the level of the high pressure circuit, or an injector blocked in the open position. To do this, and for each cylinder, the torque contribution of the engine is calculated from the signal from the speed and the angular position of the engine. This contribution is then compared to the reference contribution. This reference contribution is calculated from the injection time by the computer. If one of the values of the torque is greater than the reference contribution, the computer then diagnoses an injector blocked in the open position. This method is also valid for several injectors blocked in the open position and has the advantage of being able to identify the faulty injector. On the other hand, if all the torque values are lower than the reference contribution, then the computer will diagnose a leak in the fuel supply circuit. Finally, EP-A-1 205 657 describes a method based on the same principle as that of the preceding document, in the sense that the contribution to the torque of each cylinder is calculated. However, the diagnosis is based on the comparison between the torque provided by each cylinder to the average of the contribution of the other cylinders. The difference between the torque provided by each cylinder to the average of the contribution of the other cylinders is called "index balance", and is denoted ISfi.

  If the pressure of the injection rail becomes lower than a threshold, then the computer stores the value of ISfi then cuts the injectors and closes the flue gas recirculation valve (EGR). The "unbalance index" is then calculated again after a given time, then a criterion representing the difference of "unbalance index" before and after cutoff injectors is compared to a theoretical criterion. If the criterion is lower than the theoretical criterion, then the system diagnoses a leak in the high pressure circuit. On the other hand, if the criterion is higher than the theoretical criterion, then an injector is diagnosed in the open position. In other words, this diagnosis is based on a relative comparison of the contributions to the torque of each injector. In view of this state of the art, the present invention aims to provide a method of detecting an injector blocked in the open position, without having to generate additional protection costs related to the use of an additional sensor as described. in EP-A-0 785 349. Another object of the invention is to allow such detection every quarter cycle for a four-cylinder engine, which allows to detect the possible leakage of the four injectors on two complete turns. Another object of the invention is to provide a method which does not have to be applied after detection of loop deviation of the rail pressure, so as to obtain a higher detection speed than the solutions described in the commented documents. upper. In other words, the present invention allows the detection of a much lower level of injector leakage than that detectable with a diagnostic on the loop gap of the rail pressure, thus optimizing the engagement of degraded modes. set up to protect the engine and the driver. Moreover, if a loop gap is detected on the rail pressure (rail pressure measured much lower than the rail pressure setpoint), which is then not coupled to an injector leakage detection by the present method, it can then be concluded that possibility of external leakage. And so, again, we have the advantage of being able to engage the degraded modes best suited to the situation. Finally, an object of the invention is to allow the implementation of a continuous diagnostic process which, given the harmful consequences caused by an injector blocked in the open position, is of great interest.

  The present invention therefore relates in the first place to a method for diagnosing an injector leak in an injection system of an internal combustion engine fitted to a motor vehicle, provided with a number n of cylinders, this injection system comprising a number n of injectors that send

  each of the fuel to a respective cylinder of the engine, i being between 1 and n.

  This process is remarkable in that it comprises the following steps which consist of:

  a) determining a phase of absence of voluntary injection of fuel into the engine;

  b) during this phase, and for each of the cylinders, determine the corresponding average gas torque representative of the contribution of this cylinder to the output torque of the engine;

  c) comparing the value of this average torque, or a variable depending on this torque, to a reference value;

  d) diagnose a state of leakage when a mathematical relationship between this torque value or this variable and the reference value is verified.

  By the term "phase of no voluntary injection" is meant a period of time during which the driver does not actively solicit the engine, in particular by pressing the accelerator pedal.

  According to other advantageous and nonlimiting features of this process:

  a voluntary no-injection phase is determined which corresponds to a lack of biasing of the accelerator pedal of the vehicle, for example to a lifting phase of the foot of the driver of said vehicle;

  it is verified that this phase of absence of voluntary injection is outside a phase of registration of the injectors;

  in step c), comparing the value of the torque with a reference torque value and in step d), a leakage state is diagnosed when this value of the torque is greater than the reference torque value;

in step c):

  ci) we calculate an average value given by the following relation: _1 Cimoye, t = ù (Ci) n

  c2) for each cylinder, calculate the torque deviation AC, given by the following relation: ACi = Ci-Cin, oven c3) when this torque difference is greater than a predetermined threshold, a leakage state is diagnosed for the corresponding injector; when a state of leakage is diagnosed within a given injector, it controls a reduction of the fuel flow within it; the average gas torque is determined by using a position sensor to detect the displacement of the patterns of a target secured to an element of the moving motor in rotation, said sensor delivering an alternating frequency signal proportional to the speed of displacement of the target; said steps are carried out continuously; a degraded operation mode of the engine is determined by comparing the result of the diagnosis with other engine diagnostics. Another aspect of the invention relates to a device for implementing the method according to one of the preceding characteristics.

  This device comprises: first means for determining a position of the accelerator pedal of the vehicle corresponding to a lack of stress on the latter by the driver; second means for determining whether no request for injection takes place during the phase of absence of solicitation, following resetting strategies; third means for determining the pressure in a fuel supply rail; fourth means for determining a loop gap of the rail pressure; fifth means for determining the torque of the cylinder representative of the output torque of the engine. Other features and advantages of the invention will emerge from the following description of a detailed embodiment. This description will be made with reference to the accompanying drawings in which: - Figure 1 is a simplified view of an engine to which the method and apparatus of the present invention are applicable; Figure 2 is a block diagram illustrating the operation of the method according to the invention; FIGS. 3 and 4 are flow diagrams schematically illustrating two variants of the diagnostic method according to the invention.

  In Figure 1 is shown a combustion engine which is applicable to the method according to the invention. This engine comprises at least one movable piston 4, a connecting rod 5, a combustion chamber 3, a gas intake device 2, a gas exhaust device 1, means for measuring the angular position of the crankshaft 7, at the less an injector 8 (or Bn), a device (12) connecting the injector 8 to pressurized fuel, means for measuring the pressure of the fuel 10, means for measuring the temperature of the fuel 11, and a housing 6 to control the entire system. The position of the accelerator pedal 9 of the vehicle allows the electronic unit 6 to control the engine according to the will of the driver. As shown in FIG. 2, the electronic unit 6 comprises means which, when the operating conditions of the engine as well as lifting conditions with respect to the accelerator pedal 9, are verified, are capable of carrying out a test leak detection of each of the injectors of the engine, this by calculation of the corresponding average torque, torque representative of the contribution of this cylinder to the output torque of the engine and, if this test is conclusive, to limit depending on the response, the fuel injection rate. To do this, this device comprises first means 90 for determining a position of the accelerator pedal 9 of the vehicle corresponding to a lack of stress on the latter by the driver. It comprises second means 91 for determining whether no injection request takes place during the phase of absence of solicitations, following strategies for resetting the injectors. It further comprises third means 10 for determining the pressure in a fuel supply rail, as well as fourth means for determining a loop gap of the rail pressure. Finally, it comprises fifth means for determining the average torque Ci of the cylinder Ai representative of the contribution of this cylinder to the output torque of the engine. In a preferred embodiment, this device also comprises sixth means for determining the cooling water temperature of the engine and checking whether it is higher than a determined threshold. The method according to the present invention therefore implements the determination of the average gas torque of each of the cylinders of the engine. A method for determining this torque is described in the French patent application No. 06 55767 of the present applicant.

  For the record, two embodiments will be recalled hereinafter.

  The device for measuring the gas torque, connected to a magnetorestructing sensor 140, is composed first of all of means for performing a reversal of the durations, in order to calculate the instantaneous angular speed of the engine co (t) of the flywheel 14 connected to the shaft. motor 13. These means are connected to means which will perform the correlation between the set of measurements of the instantaneous angular velocity cok, obtained at each pulse of the position sensor or sampled by a computer, via a sensor speed, and the average value of the indicated torque Cgaz, o (or C ;, as indicated later in the description and the claims).

  Thus, the method of measuring the torque implemented by this device performs the following different steps:

  It calculates the instantaneous angular velocity co (t) of the flywheel 14 from the measurement of tooth duration At of the ring gear associated with the flywheel, which it reverses and multiplies by the corresponding angle of the passage of the tooth .

  The aforementioned means perform a reversal of the duration Atk of the teeth of the position sensor. This duration corresponds to the time that elapses between a rising or falling edge of the signal emitted by the position sensor and the next edge. This duration is associated with the tooth Dk, angular position 0k, angular width 00k of the flying target. The angular velocity (Ok associated with the tooth Dk is then obtained by inverting the duration Atk as expressed by the equation El: wk = A9k (El) Atk The correlation means realize the correlation between the average gas torque Cgaz, o and the instantaneous speeds cok.

  For this, the device performs the following actions:

  Multiplication and summation of the instantaneous speeds cok by coefficients ak, in order to calculate the average torque indicated according to the equation E2.

Cga ,, o = akwk (E2) k = q

in which :

Cga ,, o = average torque indicated;

  GJk = instantaneous speed associated with tooth Dk;

  ak == weighting coefficient of the speed associated with tooth Dk; Q and r = numbers of the teeth of the ring gear, counting as tooth number 1 the first tooth following the TDC of the cylinder before the combustion phase. The ring gear having N teeth, q and r may be greater than N, depending on the number of combustions, s taken into account for the calculation of the indicated torque q and r then designate the number of teeth moving past the sensor. 2 r thus includes an integer number of PMH and thus counts an integer number of combustions. s is an integer representing the number of combustions taken into account in the calculation of the indicated torque. The larger the value, the higher the value obtained by the average indicated torque. In particular, it is thus possible to estimate the indicated average torque developed by the cylinder u of an assembler comprising p cylinders, according to the equation E3:

  where: [Cg z o = indicated average torque of the cylinder u during a combustion cycle; wk = instantaneous speed associated with tooth Dk; ak == weighting coefficient of the speed associated with tooth Dk; qa = number of the first tooth following a PMH linked to the combustion phase of the cylinder u of the engine; The tooth number such that: ## EQU1 ## therefore includes the combustion phase of the cylinder u and corresponds to the number of the tooth bonded to the PMB according to the PMH of the cylinder u. The calculation of the average torque indicated according to the approach of equation E2 has the following advantages: q = number of the first tooth following a PMH linked to the combustion phase of one of the cylinders of the engine; r = number of the tooth such that: ruq = sN 20 25 The angles Ok of the teeth Dk of the flying target can be arbitrary. In particular, the calculation of the indicated torque, thus achieved, is not affected by:. angular defects of the target; . problems of wrong round; . the size of the long tooth; . the defects of the filtering electronics of the sensor signal (phase shift of the fronts after a long tooth); because it integrates pisa in account of these defects in the coefficients Ik. The coefficients Ik are dependent, in the first order, on the average speed of the motor wo. Mapping or a regime dependent function for calculating coefficients kk is therefore necessary. It is also possible to depend on the coefficients (XI (of the engine's environmental parameters (EGR rate, phase of the injections, quantity of fuel injected, compressor outlet air temperature, exhaust gas temperature, temperature of the recycled gas EGR, water temperature, oil temperature, temperature before turbine, pressures of the intake manifold or the exhaust manifold ...).

  According to a second embodiment, the device for measuring the gas torque, connected to the magneto-reluctant sensor 140, is composed firstly of means making a measurement of the durations of the teeth of the flywheel 14. These means are then connected to means which will realize the correlation between the set of measurements of instantaneous angular duration Atk, obtained at each pulse of the position sensor, and the average value of the indicated torque Cgaz, o. Thus, the method of measuring the torque used by this device performs the following steps: It calculates the instantaneous angular period d (t) of the flywheel from the measurement of tooth duration At of the ring gear associated with the flywheel 'inertia.

  The means perform a measurement of the duration Atk of the teeth of the position sensor. This duration corresponds to the time that elapses between a rising or falling edge of the signal emitted by the position sensor and the next edge. This duration is associated with the tooth Dk, angular position Ok, angular width AOk of the flying target.

  The means realize the correlation between the average gas torque Cgaz.o and the instantaneous durations Atk. For this, the device performs the following actions:

  Multiplication and summation of the instantaneous durations Dk by coefficients Ik, in order to calculate the average torque indicated according to the equation El: Cg, z, o = akAtk (El) k = q

  in which: Cgaz o = average torque indicated;

  Ot ~ = instantaneous duration associated with tooth Dk;

  ak = weighting coefficient of the duration associated with tooth Dk; q and r = numbers of the teeth of the ring gear counting as tooth number 1 the first tooth following the TDC of the cylinder before the phase of

  combustion. The ring gear having N teeth, q and r may be greater than N, depending on the number of combustions, s taken into account for the calculation of the indicated torque q and r then designate the number of teeth moving past the sensor;

  Q = number of the first tooth following a TDC related to the combustion phase of one of the cylinders of the engine;

  r = number of the tooth such that: rùq = sN 2

  r therefore includes an integer number of PMH (or combustions), thereby accounting for an integer number of combustions.

  s is an integer representing the number of combustions taken into account in the calculation of the indicated torque.

  The larger the value, the higher the value obtained by the average indicated torque.

  In particular, it is thus possible to estimate the indicated average torque developed by the cylinder u of an engine comprising p cylinders, according to the equation E2:

[Cgaz, where λ = l ak & tk (E2) k = q

  wherein: [Cgaz o J, = average indicated torque of the cylinder u during a combustion cycle Otk = instantaneous speed associated with the tooth Dk; ak = weighting coefficient of tooth duration associated with tooth Dk; that number of the first tooth following a PMH linked to the combustion phase of the cylinder u of the engine; ru = number of the tooth such that N r ,, = 2 + 9a ru thus encompasses the combustion phase of the cylinder u and corresponds to the number of the tooth linked to the PMB according to the PMH of the cylinder u. The calculation of the average torque indicated according to the approach of equation E2 has the following advantages: The durations Atk and the angles A9k of the teeth associated with the teeth Dk of the flying target can be arbitrary. In particular, the calculation of the indicated torque, thus achieved, is not affected by:. angular defects of the target; 15. problems of wrong round; . the size of the long tooth; . the defects of the filtering electronics of the sensor signal (phase shift of the fronts after a long tooth); because it integrates the taking into account of these defects in the coefficients 20 ak. The coefficients ak are dependent on the first order of the average engine speed wo. A cartography or a function dependent on the regime for calculating the coefficients ak is therefore necessary. It is also possible to make the coefficients ak dependent on the environmental parameters of the engine (EGR rate, injection timing, quantity of fuel injected, compressor outlet air temperature, exhaust gas temperature, temperature EGR recycled gases, water temperature, oil temperature, turbine front temperature, intake manifold pressures or exhaust manifold ...). In Figure 3 are schematically illustrated the various steps of an embodiment of the method according to the invention. After an initialization period (block 100), it is detected whether the engine conditions are verified (block 101). This means that a phase of absence of voluntary fuel injection into the engine is detected.

  This phase typically corresponds to a lifting of the driver's foot relative to the accelerator pedal, this outside a resetting phase of the injectors. Under these conditions, the torque of each cylinder must in principle be zero or negative. If these operating conditions of the engine are verified, then each of the cylinders Ci of the engine (block 102) is selected in turn and the value of the corresponding average gas torque Ci is calculated, this torque being representative of the contribution of this cylinder to the output torque of the motor (block 103). At block 104, this value Ci is compared with a reference torque value SR and, if this torque value is greater than the reference value, the injector Ci is then diagnosed as being leaking (block 105). If not, the system is reset and a new check is made. Another variant embodiment of this method is shown in FIG. 4. Still after an initialization period (block 200), it is checked whether the operating conditions of the engine are satisfied (block 201) and the gas torque is then measured. average of each of the injectors Ci (block 202). In a next step (block 203), the average value C max is calculated which is equal to n E C; , where n is the total number of cylinders. The torque deviation is then calculated to the average value which is calculated for each cylinder with the expression of the block 204, namely AC; = C ùC meansA block 206, when this difference is greater than a predetermined threshold ACmax, the injector in question is declared leaking and strategies to limit its flow can be activated. If not, the system is reset and a new check is made.

Claims (10)

  1. A method for diagnosing an injector leak in an injection system of an internal combustion engine fitted to a motor vehicle, provided with a number n of cylinders, this injection system comprising a number n of injectors B each sends fuel to a respective cylinder Ai of the engine, i being between 1 and n, characterized in that it comprises the following steps which consist in: a) determining a phase of absence of voluntary fuel injection in the rnoteur; b) during this phase, and for each of the cylinders Ai, determine the corresponding average gas torque Ci representative of the contribution of this cylinder to the output torque of the engine; c) comparing the value of this pair Ci, or a variable function of this pair, with a reference value; d) diagnose a state of leakage when a mathematical relationship between this torque value or that variable and the reference value is verified.   2. Method according to claim 1, characterized in that a determined phase of absence of voluntary injection which corresponds to a lack of bias of the accelerator pedal (9) of the vehicle, for example to a phase of lifting of the foot on the part of the driver of said vehicle. 20   3. Method according to claim 2, characterized in that it is verified that this phase of absence of voluntary injection is outside a resetting phase Br11 injectors.   4. Method according to one of claims 1 to 3, characterized in that in step c) the value of the torque Ci is compared to a reference torque value Sr and that in step d), a leak state is diagnosed when this value of the torque Ci is greater than the reference torque value Sr.   5. Method according to one of claims 1 to 3, characterized in that in step c): cl) is calculated a mean value Cimoy given by the following relationship: 1 = Cimoyen = ù (ECi) nc2 ) for each cylinder Ai, the torque deviation A Ci given by the following relation is calculated: AC, = Ci-Cinroyen c3) when this torque difference is greater than a predetermined threshold, a leakage state is diagnosed for corresponding injector.   6. Method according to one of the preceding claims, characterized in that when a leakage state is diagnosed within a determined injector Bi, it controls a reduction of fuel flow within it.   7. Method according to one of the preceding claims, characterized in that the average gas torque Ci is determined by using a position sensor (140) to detect the displacement of the patterns of a target attached to an element of the rotating motor (14), said sensor (140) providing an alternating frequency signal proportional to the speed of movement of the target.   8. Method according to one of the preceding claims, characterized in that it renews regularly. implementation of said steps.   9. Method according to claim 1, characterized in that a degraded operating mode of the engine is determined by comparing the result of the diagnosis with other diagnostics of the engine.   10. Device for carrying out the method according to any one of the preceding claims, characterized in that it comprises: first means (90) for determining a position of the accelerator pedal of the vehicle corresponding to an absence of solicitation of it from the driver; second means (91) for determining whether no request for injection takes place during the phase of absence of solicitation, following resetting strategies; third means (10) for determining the pressure in a fuel supply rail; fourth means for determining a loop gap of the rail pressure; fifth means for determining the average gas torque Ci of the cylinder Ai, representative of the contribution of this cylinder to the output torque of the engine.