FR3034469A1 - VEHICLE DIAGNOSTIC METHOD ON A VEHICLE RELATING TO A PRESSURE FAILURE OF THE CYLINDER PRESSURE - Google Patents

Abstract

On-board diagnostic method comprising the following steps: • after detection (10) of the cylinder pressure acquisition error adopting the shape of an unlikely pressure peak in the cylinder, • the control unit motor engages a compression test (30) in the cylinder having a cylinder pressure sensor, using a signal from the crankshaft position sensor, and: - if the compression test results in incorrect compression in the cylinder, then engine control unit registers (41) a compression failure diagnosis in that cylinder, and - if the compression test results in a correct compression in the cylinder, then the engine control unit records (42) a failure diagnosis said cylinder pressure sensor system.

Description

The present invention relates to an on-board diagnostic method comprising a motor control unit, a motor equipped with a cylinder pressure sensor system comprising at least one cylinder pressure sensor arranged in a cylinder and a control system. exploiting the signal from said cylinder pressure sensor, and an angular position sensor of the engine crankshaft, said onboard diagnostic method comprising a step of performing an error diagnosis of acquisition of the cylinder pressure in the cylinder having the cylinder pressure sensor. Such a diagnostic method is used in a known manner to monitor the pressure in a cylinder from the cylinder pressure sensor mounted in the cylinder. The engine control unit monitors in real time the signal coming from the cylinder pressure sensor and in particular a failure as soon as the signal for the acquisition of the cylinder pressure conveys an improbable pressure peak in the cylinder, evaluated in the context of a plausibility diagnosis of the measured cylinder pressure peak itself falling within the category of cylinder pressure acquisition error diagnostics. By improbable pressure peak is meant a pressure that does not correspond to an expected or modeled pressure. Displaying an error diagnosis on the vehicle dashboard normally means that a pressure failure has been detected in the cylinder with the cylinder pressure sensor. Such a pressure failure may be due to a lack of tightness of the cylinder, for example due to broken or worn segments, a valve that no longer closes or closes incorrectly, etc ... However, there is another due to detection of an improbable pressure peak in the measured cylinder, which may come from the cylinder pressure sensor itself and / or its controller including the signal operating system from the cylinder pressure sensor, itself failing, these bodies being subsequently and if necessary referred to together under the term "cylinder pressure sensor system". According to the current state of the art, it is thus not possible to discriminate the real cause at the origin of a diagnosis of error of acquisition of the cylinder pressure translated by the detection of an unlikely pressure peak . In the event of a faulty pressure in the cylinder, it would nevertheless be necessary for the engine control unit to be able to take certain measures, for example to limit or even cut the injection into the latter, in particular in the case of a direct injection, in order to reduce the pollutants released by the vehicle exhaust via the defective cylinder, until the return of it to the garage.

Indeed, in the case of a faulty pressure in a cylinder, combustion does not occur normally in the latter, a significant release of unburned hydrocarbons is particularly noted in case of maintenance of the injection. On the other hand, it is useless, or even counterproductive, to cut the injection if the failure of the detected cylinder pressure is not caused by a failure of the cylinder pressure. The present invention proposes to overcome this disadvantage. More precisely, it consists, in the context of the application described above, in a method characterized in that it further comprises the following steps: after a detection of a cylinder pressure acquisition error adopting the shape of an unlikely pressure peak, in a cylinder having a cylinder pressure sensor, - the engine control unit engages a compression test using a signal from the crankshaft position sensor, and: - if the compression test of the motor results in incorrect compression in the cylinder having a cylinder pressure sensor, then the engine control unit records a diagnosis of compression failure in the cylinder, and - if the engine compression test results in a correct compression in the cylinder having a cylinder pressure sensor, then the engine control unit records a failure diagnosis of said cylinder pressure sensor system Indre. The method according to the invention can be implemented by means of appropriate software implemented for example in an engine control unit. Thus, such a method does not require any additional component. The method according to the invention allows the motor control unit to take any appropriate arrangement in the case of such an error detection of cylinder pressure acquisition, and in particular to discriminate operating modes. degraded, by activating the most appropriate. According to an advantageous characteristic, said compression test is engaged at the next start of the engine following the detection of an error of acquisition of the cylinder pressure. According to an advantageous characteristic, the compression test engaged using the crankshaft position sensor consists in evaluating the compression in the cylinder after synchronization of the engine and under the starter, having prevented any injection of fuel into at least said cylinder comprising the cylinder pressure sensor.

According to an advantageous characteristic, the compression test engaged by using the crankshaft position sensor comprises a step of evaluating the mean time that passes between at least two consecutive teeth of a crankshaft target of said crankshaft position sensor. crankshaft.

According to an advantageous characteristic, the compression test engaged using the crankshaft position sensor comprises a sequence comprising at least two different measurements of the time which elapses between two consecutive teeth of the crankshaft target of said crankshaft position sensor. and further comprises a step of comparing said at least two measurements obtained to an on-board model previously recorded in the engine control unit. Other features and advantages will become apparent on reading the following of an exemplary embodiment of a method according to the invention, accompanied by the accompanying drawings, an example given by way of nonlimiting illustration. FIG. 1 represents a logic diagram of an exemplary embodiment of a method according to the invention of on-board diagnostics on a vehicle. FIG. 2 represents a logic diagram of an exemplary embodiment of a compression test. FIG. 3 represents an image of the evolution curve of the crankshaft speed obtained from the crankshaft position sensor signal, obtained during an example of a compression test. The flow chart shown in FIG. 1 is an example of a on-vehicle diagnostic method (not shown) comprising an engine control unit, a motor equipped with a cylinder pressure sensor system comprising at least one cylinder pressure sensor. disposed in a cylinder and a signal operating system from the cylinder pressure sensor, and an angular position sensor of the crankshaft of the engine, the onboard diagnostic method comprising a step of performing a diagnosis of error acquisition of the cylinder pressure in the cylinder provided with the at least one cylinder pressure sensor. The process shown comprises the following steps: step 10: the engine control unit detects a cylinder pressure acquisition error, taking the form of an improbable pressure peak in the cylinder with the cylinder pressure sensor, following a plausibility analysis of the pressure peak in this cylinder, 35 - step 20: after detection of the error in step 10, the engine control unit starts a discrimination sequence, the first step 21 consists of monitor the next event of change of state of the key or the like of 3034469 4 vehicle contact: at the next change of state of the ignition key or the like from the off state "off" to the ignition state put "on The following step 30 is then used consisting in carrying out a compression test: Step 30: During a test phase preceding the normal starting of the engine, ie under the starter after synchronization of the motor. r but before the start-up phase itself under starter comprising fuel injections of the cylinders in order to reach the engine speed, a compression test is carried out which will be detailed later, using a different means of the sensor of the engine. pressure cylinder, for example the crankshaft position sensor, consisting in verifying that the pressure normally moves in the cylinder comprising the cylinder pressure sensor at the origin of the cylinder pressure error detection, that is to say ie to essentially check that the gas is compressed correctly in the cylinder in the compression phase, - step 40: at the end of the compression test, the engine control unit can pronounce on the fact that the compression of the gas is normal or not in the cylinder: the process then continues according to the following steps: step 41: if the compression is incorrect or abnormal in the cylinder comprising the sensor Cylinder pressure, then the engine control unit records a compression failure diagnosis in said cylinder, and step 42: if the compression is correct or normal in the cylinder having the cylinder pressure sensor, then the engine control unit records a failure diagnosis of the cylinder pressure sensor system, which may for example be a failure of the cylinder pressure sensor and / or its controller / operating system. In the case of compression in the incorrect or abnormal cylinder (step 41), the engine control unit after having advantageously recorded this loss of compression cylinder in the OBD register (for "On Board Diagnostic" in English), will compensate, for example, by advantageously limiting or cutting the injection of fuel into this cylinder in order to ensure optimal engine behavior in order to limit the emission of pollutants as much as possible, for example by activating a so-called "limp home" mode of operation, that is, a degraded mode of operation of the motor until the repair of the fault causing the loss of compression. Such degraded modes of operation are known to those skilled in the art and will not be described in more detail here. In the case of a compression in the correct or normal cylinder (step 42), the engine control unit after having advantageously recorded this error of the cylinder pressure sensor system in the OBD register, can start the engine by activating a mode of operation known as "limp home" mode, that is to say a degraded operating mode of the engine, allowing it to operate with a failure of the cylinder pressure sensor system; such a degraded mode operation procedure may for example consist of replacing the information previously given by the cylinder pressure sensor with a cylinder pressure model recorded in the engine control unit until the repair of the failure is carried out. the origin of this failure of the cylinder pressure sensor system. Such degraded modes of operation are known to those skilled in the art and will therefore not be described in more detail here. Additionally, the engine control unit can inform the driver with the compression test result, as indicated above, for example by means of a display on the dashboard. The compression test, as will be explained later, is a test which is advantageously carried out before the start-up phase of the vehicle because it requires the cutting of the injection at least in the cylinder under test. Such a test, when activated, therefore delays the start-up phase itself and the establishment of the established regime. A compression test could be started immediately after the detection of a cylinder pressure acquisition error as described above, but this could only validly be carried out in the deceleration or standing up mode, because the need to cut the fuel injection into the cylinder under test, long enough to make the diagnosis more robust. This range corresponding to a deceleration rate of the engine or foot lifted is however increasingly occupied by different functions of the engine control unit.

Therefore, it is preferred that the compression test step 30 be carried out immediately after the next change of state of the ignition key or the like of the vehicle, from the "cut off" position to the "established contact" position. During the rotation of the starter and after synchronization of the engine, so that the engine control unit can identify the crank position setting via its position sensor, with respect to the engine cycles, in particular by compared to compressions, in this case a compression test. Thus, the compression test is advantageously engaged at the next start of the engine following the detection of an error of acquisition of the cylinder pressure. This compression test therefore advantageously consists in using the crankshaft position sensor to evaluate the compression in the cylinder comprising the cylinder pressure sensor, after engine synchronization and under starter, having cut off any injection of fuel into it. all cylinders to prevent engine start while the compression test is in progress. An exemplary embodiment of the compression test will now be described with the help of Figures 2 and 3.

Step 31 is to ensure that the conditions for engaging a compression test are met. For this purpose, the engine control unit verifies that no component required for the compression test fails, that is to say no component providing the engine temperature (coolant temperature sensor), the pressure atmospheric (intake pressure sensor), the battery voltage (battery voltmeter). If all the necessary components are operational, the process proceeds to the next step 32. If a component is not operational, the process is returned to step 10, after recording the detected component failure, and the failure of the compression test. Step 32 consists in making a system intervention request. This system intervention consists in taking control of the motor by intervening on the actuators to allow the compression test to run under optimal conditions. The system intervention is in practice to cut and lock the fuel injection via the injectors, so that none of the cylinders of the engine is supplied with fuel, and thus prevent engine starting. For this purpose, the engine control unit 20 will further preferably act on the butterfly valve and exhaust gas recirculation valve actuators as appropriate, closing both valves to improve the performance of the compression test. The next step 33 is to verify that the system intervention request has been applied. This step 33 is to set a time period that allows the system time to proceed with the operations defined in step 32, and to verify at the end of this time that all these operations have been completed successfully. For example, to verify by reading back the position that the butterfly valve is closed properly. If the system intervention request could not be applied or failed, the process returns to step 10 after recording the failure of the system intervention request. If step 33 is passed successfully, the process proceeds to the next step 34. Step 34 consists of activating the engine starter. This step 34 is implemented by the driver who actuates the engine start, and the method, via the engine control unit, waits for this event. When the driver actuates the starter, the compression test proceeds to the step of evaluating the compression in the cylinder (s) having a cylinder pressure sensor on which an error of acquisition of the cylinder has been detected. cylinder pressure as described above. For the rest, we will consider a single cylinder pressure sensor in a cylinder. To do this, the engine control unit performs a compression test sequence as follows: using the crankshaft position sensor, the signal from that sensor, the compression test includes a step of evaluating the time that flows between at least two consecutive teeth of a crankshaft target of the crankshaft position sensor. A crank position sensor, for example Hall effect or inductive is widely known to those skilled in the art and will not be described in detail here. Recall simply that it consists of a target secured to the crankshaft and having a determined number of teeth distributed over a turn of the target, that is to say one revolution of the crankshaft, for example 60 teeth, separated respectively by 6 °, and the body of the sensor itself which detects the passage of the teeth of the target in front of him. Briefly, each time a tooth of the target rotating with the crankshaft passes in front of the inductive or Hall effect sensor, fixed with respect to the target, a signal is sent to the engine control unit. The time separating two consecutive signals corresponding to two consecutive teeth of the target is a function of the speed of rotation of the crankshaft. The faster the crankshaft rotates, the shorter the time between two consecutive signals. The measurement of this time with the knowledge of the pitch separating the teeth from the target makes it possible to obtain in particular the speed and the position of the crankshaft. The compression test consists first of all in measuring the time separating two consecutive signals corresponding to two consecutive teeth of the target, this during at least the whole compression phase, and preferably also during the subsequent expansion phase, which is possible from the moment the motor is synchronized, in order to advantageously define an image profile of the compression in the cylinder on the compression / expansion phases. The sequence comprises measurements over several cycles of rotation of the crankshaft until a result representative of the reality of the compression in the cylinder studied is obtained. This may for example mean that the test evaluates the compression over at least about ten compression / expansion cycles in the cylinder to then average the measured values.

As shown in FIG. 3 with the curve 2 illustrating an image of the rotational speed of the crankshaft, under starter, during the process step, the rotation of the crankshaft is punctuated by the successive compressions and detents in the cylinders which cause relatively large rotational speed variations thereof. Indeed, when the piston in the cylinder is in the compression phase, the rotation of the crankshaft requires more energy than in the other phases of the cycle and the rotation speed therefore decreases with respect to an average rotation speed of the crankshaft, while the rotational speed of the crankshaft accelerates in the expansion phase with respect to this same average crankshaft rotation speed, because of the energy accumulated by the compression of the gas in the cylinder, this for a given power of starter . The average speed reference corresponds for example substantially to the speed of the crankshaft at the top dead center of exhaust (for a given cylinder), but can be any other average speed by definition. In FIG. 3, a chronological time scale is represented on the abscissa, and the time T in milliseconds (ms) separating the passage of two consecutive teeth from the target in front of the sensor. The points of the curve 2 10 represent successive continuous occurrences during the time of measurement of the time separating two consecutive teeth of the crankshaft (for example taken from the synchronization and when the rotational speed of the crankshaft under starter has stabilized) . Of course, when the rotational speed of the crankshaft is maximum, the time separating two consecutive teeth from the target is minimal, and when the rotational speed of the crankshaft is minimal, the time separating two consecutive teeth from the target is maximum. The tested engine comprises four cylinders CYL 1, CYL 2, CYL 3, and CYL 4. For each cylinder, the curve 2 represents the maximum average Tmax and the minimum average Tmin of the time reached between two consecutive teeth, respectively corresponding substantially at the top dead center of compression and the bottom dead center of relaxation. Recall that the average time reached between two consecutive teeth means an average of the measured time between two consecutive specific teeth, measured over several successive motor cycles. For such an engine as shown, it is noted that the portion of curve corresponding to cylinder CYL 4 with a cylinder pressure sensor, shows an anomaly when compared to the parts of curve 2 obtained for the other three cylinders CYL 1, CYL 2, and CYL 3. Indeed, the CYL 4 part of the curve does not show a normal maximum increase in the time separating two consecutive teeth, nor a normal decrease of this time which follows it because of the crankshaft acceleration in the relaxation phase after compression. In other words, the differential 30 between the maximum Tmax and the minimum Tmin for the cylinder CYL 4 is too small compared to the same differential in the other cylinders. The differential between the maximum Tmax and the minimum Tmin for the cylinder CYL 4 is representative of a lack of compression or compression too weak, abnormal or incorrect. This differential may advantageously serve as a reference for evaluating the compression efficiently and quickly. Curve 2 is representative of a compression profile in each cylinder CYL 1, CYL 2, CYL 3, and CYL 4 of the engine during the compression test. Note that when a cylinder pressure acquisition error is detected as described above, the engine control unit may preferably perform a compression test on each of the engine cylinders, as shown in FIG. 3. The compression test method may, alternatively and in practice, consist in retaining for the evaluation of compression only the Tmax 5 and Tmin measurements for the cylinder under test. The compression thus evaluated in the cylinder CYL 4 tested with a cylinder pressure sensor can be compared to a reference compression, in the next step 37 of the method, so that the engine control unit can provide the from this comparison, a diagnosis of the actual compression in the cylinder tested. In step 37, the compression measured and definitively retained at the end of the test is compared, for example, with the compression obtained for another cylinder CYL 1, CYL 2, CYL 3, which is the preferred solution, or to a normal or correct compression model previously recorded in the engine control unit for the cylinder CYL 4. As explained above, the compression test preferably calculates the difference between Tmax and Tmin, ie Tmax-Tmin, in the cylinder tested, and compares the difference value obtained with an onboard model difference between Tmax and Tmin for an identical cylinder whose compression is normal or correct. The following system data will preferably be used in order to apply, if appropriate, a compensation to the obtained values of compression evaluation, preferably to the measured Tmax and Tmin values: coolant temperature, crankshaft speed, flow rate. air intake, Tmax and Tmin being variable according to these parameters. At the end of the comparison, again at step 37 in FIG. 2, the engine control unit decides the final result of the compression test sequence accomplished, for example by positioning the difference Tmax-Tmin measured by ratio to a threshold Threshold of acceptability defined and recorded beforehand, in order to diagnose whether the compression in the cylinder is normal or correct, or on the contrary if the compression in the cylinder is abnormal or incorrect, depending on whether the measured difference is a either side of the Tseuil threshold. If the difference Tmax-Tmin measured is, for example, less than Thresh, the motor control unit then records a detected compression loss diagnosis (step 40) as described above with the help of FIG. 1. In the figure 2, there is shown a step 36 of the method, which consists in monitoring that the operations defined by the system intervention request applied, described above in steps 32 and 33, are well maintained throughout the course of the sequence of compression test, for example, monitor that the butterfly valve is kept closed. If so, the final result of the test is validated, and in the negative the result of the test is invalidated and the process returns to step 31 (not shown) to recommence a compression test.

Claims (5)

REVENDICATIONS1. On-board diagnostic method comprising a motor control unit, an engine having a cylinder pressure sensor system comprising at least one cylinder pressure sensor disposed in a cylinder and a signal operating system derived from said cylinder sensor. cylinder pressure, and an angular position sensor of the engine crankshaft, said onboard diagnostic method comprising a step of performing an error diagnosis of acquisition of the cylinder pressure in the cylinder with the cylinder pressure sensor, characterized in that said method further comprises the following steps: - after a detection (10) of an error of acquisition of the cylinder pressure adopting the shape of an improbable pressure peak, in a cylinder comprising a cylinder pressure sensor, - engine control unit engages a compression test (30) using a signal from the crankshaft position sensor, and: if the engine compression test results in incorrect compression in the cylinder having a cylinder pressure sensor, then the engine control unit records (41) a diagnosis of compression failure in the cylinder, and - if the compression test of the engine results in a correct compression in the cylinder having a cylinder pressure sensor, then the engine control unit records (42) a fault diagnosis of said cylinder pressure sensor system. The method of claim 1 wherein said compression test (30) is engaged at the next engine start following the detection (10) of a cylinder pressure acquisition error. The method according to one of claims 1 or 2, wherein the compression test (30) engaged using the crankshaft position sensor is to evaluate the compression in the cylinder after synchronization of the engine and under starter, having prevented any injection of fuel at least into said cylinder having the cylinder pressure sensor. The method of any one of claims 1 to 3, wherein the compression test (30) engaged using the crankshaft position sensor comprises a step of evaluating the time elapsing between at least two consecutive teeth. a crankshaft target of said crankshaft position sensor. 3034469 12 The method of claim 4, wherein the compression test (30) engaged using the crankshaft position sensor comprises a sequence comprising at least two different measurements of the average time that elapses between two consecutive teeth of the target of the crankshaft. crankshaft of said crankshaft position sensor, and further comprises a step of comparing said at least two measurements obtained to an on-board model previously recorded in the engine control unit.