Method for predictive maintenance of a crankshaft sensor with a normalised signal

Abstract

The invention relates to a method for predictive maintenance (P) of an angular position sensor (S) for a crankshaft (A) intended to be activated by a starter powered by a battery, the sensor being intended to generate a voltage signal that comprises falling edges corresponding to the detection of rising edges of a series of teeth on a gear that rotates with the axis of rotation of the crankshaft, the method being carried out by a computing unit (Uc) configured to detect a rising or falling edge of the voltage signal, the method comprising the following steps, implemented after detecting the startup of the vehicle: / a / measuring (Em) a voltage value of the battery when the crankshaft is activated; / b / acquiring (Ea) a first current rotational speed of the crankshaft by processing the voltage signal, after detecting the startup of the vehicle; / c / generating (Eg) an alarm when the first determined rotational speed exceeds a predetermined threshold value for the battery voltage value.

Description

[0001] Description METHOD FOR PREDICTIVE MAINTENANCE OF A CRANKSHAFT SENSOR WITH STANDARDIZED SIGNAL Field of the invention

[0002] The present invention relates to the field of predictive maintenance of parts associated with a piston thermal engine. It relates in particular to the predictive maintenance of the rotation sensor of a crankshaft of such an engine.

[0003] Prior art

[0004] The combustion cycle of an internal combustion engine comprises several phases whose occurrence is staggered in time for each cylinder, the synchronized control of the valves of the thermal engine being carried out by the camshaft.

[0005] In order for the combustion cycle to proceed normally, it is necessary to have a reliable angular reference on the basis of which each phase of each cylinder is determined.

[0006] The camshaft is rotated by the crankshaft. The crankshaft is a mechanical device that, through a connecting rod, transforms the rectilinear movement of a piston into a continuous rotational movement, and vice versa, thus ensuring the transmission of the combustion energy of the fuel in the cylinders into mechanical energy.

[0007] Thus, knowing the angular position of the crankshaft makes it possible to know a reliable angular reference on the basis of which each phase of each cylinder is determined.

[0008] Such a reference is available via a toothed wheel, also called a crankshaft target, which rotates with the crankshaft. The wheel is associated with a dedicated sensor, called a crankshaft sensor, whose ultimate role is to determine the angular position and rotation speed of the toothed wheel. The sensor is equipped with a sensitive element. In one example, the wheel is metallic and the sensitive element is capable of detecting metal, such as a Hall effect sensor. The profile of the wheel typically includes a target which is provided with markers, also called teeth, distributed around its periphery. The function of the crankshaft sensor is to transform the magnetic field measured using an internal magnet into an electrical signal. According to the state of the art, some sensors are connected to the control unit by three wires (ground, power supply and signal) and have the capacity to determine the direction of rotation of a crankshaft target.

[0009] As illustrated in Figure 1, which shows a standardized signal graph in the lower part, the passage of a tooth of the gear associated with the crankshaft generates an electrical pulse of a predetermined duration on the signal wire. More precisely, the passage of a mechanical rising edge corresponds to the generation of an electrical falling edge, while the passage of a mechanical falling edge is ignored.

[0010] The predetermined duration is representative of the direction of rotation. A forward direction of rotation is illustrated on the left side of the figure and the predetermined duration of the pulse is then typically 45 us for one direction of rotation. A reverse direction of rotation is illustrated on the right side of the figure and the predetermined duration of rotation is then typically 90 ps for one direction of rotation. The crankshaft sensor is typically mounted near the flywheel which serves as a rotating target or supports such a target.

[0011] The rotating target has a signature, also called a long tooth or gap, formed by a singularity in the (otherwise regular) profile usually corresponding to two missing marks, and which allows a reference to be set for the crankshaft position. Such a signature generates a signal different from the other marks, which makes it possible to determine when the rotating target has completed a complete rotation.

[0012] A commonly used rotating target consists of 60 marks distributed around the periphery of the rotating target, and two consecutive marks removed to create the signature. Such a target is called a 60-2 rotating target. Another known rotating target is the 36-2 rotating target (36 marks plus two missing marks).

[0013] The rotation of the rotating target causes periodic changes in the magnetic flux due to the passage of the markers, which are transformed by the sensor into voltage variations that can then be sent to the engine management computer. The voltage variations include rising and falling edges forming a periodic signal synchronized with the passage of the markers in front of the sensor.

[0014] From the voltage data produced by the crankshaft sensor, the person skilled in the art knows how to calculate the rotational speed and the angular position of the crankshaft to obtain the basic data necessary for determining the injection point and adjusting the ignition advance point.

[0015] However, as the sensor ages, its magnetic effect diminishes. As a result, position determination using the magnet is less accurate, and teeth may appear missing after processing the electrical signal, particularly through clipping.

[0016] The control unit is usually configured to detect such an alteration in the precision of the angular positioning of the crankshaft. In such a case, the angular position of the engine can be determined from the angular position of the camshaft, but the angular position of the engine thus determined is then less precise. When a command to inject fuel into the engine cylinders or to fire the spark plugs is made at the wrong time, this results in a loss of energy. In addition, instead of producing mechanical energy useful for driving the engine, the unburned fuel during a misfire, or poorly burned, contributes to the emission of polluting gases into the atmosphere. The engine thus operates in a degraded mode: the engine warning light comes on and the vehicle must be immobilized.

[0017] An aim of the invention is to propose a method for predictive maintenance of the target rotation sensor. Presentation of the invention

[0018] To this end, according to a first aspect of the invention, a method is proposed for predictive maintenance of a crankshaft angular position sensor intended to be started by a starter powered by a battery, the sensor being intended to generate a voltage signal comprising rising and falling edges corresponding to detections of rising and falling edges of a series of teeth of a toothed wheel mounted integral with the axis of rotation of the crankshaft.

[0019] The method is implemented by a computing unit configured to detect a rising or falling edge of the signal, and comprises the following steps, implemented after detection of the vehicle starting:

[0020] • / a / measure a battery voltage value,

[0021] • / b / determine a first current rotation speed of the crankshaft by processing said voltage signal,

[0022] • / c / generate an alarm when the first determined rotation speed is greater than a predetermined threshold value for said measured battery voltage value.

[0023] In an advantageous variant, step / b / of acquiring the first current speed comprises:

[0024] • an acquisition by the sensor at a current time of a first rising edge, respectively falling edge, and a start of a time delay, then

[0025] • an acquisition by the sensor at a second current instant of a second rising edge, respectively falling edge, and a stopping of the time delay; step / b / of determining a first current rotation speed of the crankshaft being implemented by processing the value of the time delay.

[0026] Advantageously, step / c / of generating an alarm is implemented after a post-processing step in which it is determined whether the vehicle is started in a signature zone of the toothed wheel, the generation of an alarm being blocked if it is determined that the vehicle was started in the signature zone.

[0027] According to one possibility, prior to step / a / of acquiring a measurement (Em) of a battery voltage, the calculation unit undergoes a modeling step comprising a determination of a threshold value corresponding to a maximum rotation speed of the crankshaft at the instant of passage of a first tooth, for said battery voltage value.

[0028] According to a second aspect of the invention, there is provided a predictive maintenance module for a magnetic crankshaft angular position sensor intended to be started by a starter powered by a battery, the sensor being intended to generate a signal comprising electrical falling edges corresponding to detections of mechanical rising edges of a series of teeth of a toothed wheel mounted integrally with the rotation axis of the crankshaft. Only one of the mechanical edges generates an electrical edge, because its signal is more precise.

[0029] The module comprises a computing unit configured to detect a falling edge of the voltage signal. The computing unit is further configured to, after detecting the vehicle starting:

[0030] • measure a battery voltage value when the crankshaft is started,

[0031] • determine a first current rotation speed of the crankshaft, by processing said signal,

[0032] • generate an alarm when the first determined rotation speed is greater than a predetermined threshold value for said measured battery voltage value.

[0033] Brief description of the figures

[0034] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which one will refer to the appended drawings in which:

[0035] • [Fig. 1] illustrates in the lower part a voltage signal graph generated from the passage of teeth in front of a sensor,

[0036] • [Fig. 2] illustrates an embodiment of a method according to the invention,

[0037] • [Fig. 3] illustrates an embodiment of a module according to the invention and its physical environment,

[0038] • [Fig. 4] includes a graph showing the crankshaft rotation speeds of a first tooth as a function of the battery voltage value.

[0039] Detailed description of the invention

[0040] The embodiments described below being in no way limiting, it will be possible in particular to consider variants of the invention comprising only a selection of the characteristics described, subsequently isolated from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art. This selection comprises at least one characteristic, preferably functional without structural details, or with only a part of the structural details if this part alone is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art. Throughout the text, it is understood that starting the vehicle more particularly designates starting the heat engine providing propulsion for said vehicle.

[0041] There is now described, with reference to Figure 2 and Figure 3, an embodiment of a method P for predictive maintenance of a magnetic sensor S of crankshaft angular position A implemented by a calculation unit Uc, at the same time as a module M implementing a calculation unit Uc. The magnetic sensor S is for example a bidirectional sensor of the CPDD type, for Crankshaft Position and Direction Determination, capable of generating pulsed signals of voltage of different width depending on the direction of rotation of the crankshaft.

[0042] The magnetic sensor S is typically associated with a magnetic target C mounted integral with the rotation of the crankshaft A.

[0043] The computing unit Uc is configured to detect a rising edge, respectively a falling edge, of the signal.

[0044] It is thus possible to determine the direction of rotation by analyzing the signal generated by the magnetic device. For example, with the sensor in question, the falling electrical edge and the rising electrical edge are spaced apart by a duration of 45 ps when the toothed wheel moves in one direction of rotation, and by a duration of 90 ps when the toothed wheel moves in the other direction of rotation. According to the invention, the method comprises the following steps, after detecting the start of the vehicle:

[0045] • / a / measure Em a battery voltage value,

[0046] • / b / determine Ea a first current rotation speed of the crankshaft by processing the voltage signal,

[0047] • / c / generate Eg an alarm when the first determined rotation speed is greater than a predetermined threshold value for said measured battery voltage value.

[0048] The computing unit is configured to perform steps / a / , / b / , and / c / .

[0049] Steps a and b relate to the same or almost the same measurement time.

[0050] Vehicle cranking, i.e. crankshaft cranking, can be detected by acquiring the vehicle battery voltage signal. Indeed, cranking the crankshaft causes a significant voltage drop in the battery indicating the crankshaft cranking moment. Typically, the battery voltage signal is acquired every millisecond.

[0051] Step / b / of acquiring the first current speed can for example include:

[0052] • an acquisition by the sensor at a current time, of a first rising edge, respectively falling edge, and a start of a time delay, then

[0053] • an acquisition by the sensor at a second current instant of a second rising edge, respectively falling edge, and a stop of the time delay.

[0054] According to one possibility, the alarm generation step / c / is implemented after a post-processing step in which it is determined whether the vehicle is started in a signature zone of the gear wheel, the generation of an alarm being blocked if it is determined that the vehicle is started in the signature zone. The first rotational speed can be determined from the knowledge of the geometry of the crankshaft target as well as the two current times of edge detection. For example, by denoting tl the first current time and t2 the second current time, when the target is a 60-2 target, the speed is on average 6 / (t2-tl) when the start is performed outside the signature zone.

[0055] Prior to step / a / of measuring a voltage value, the calculation unit may undergo a modeling step (Ei) in which said threshold value of the first rotation speed is determined, as a function of the battery voltage value.

[0056] The alarm generation step / c / can be followed by a replacement step Er of the crankshaft sensor S carried out by a human operator.

[0057] According to one embodiment, the modeling step can be carried out prior to the implementation of the method according to the invention, for example on a test vehicle representative of another vehicle equipped with the module M according to the invention. According to a variant, the calibration step can be implemented on a vehicle whose crankshaft magnetic sensor S is new, for example after the replacement of the magnetic sensor.

[0058] Figure 4 illustrates an example of a graph whose x-axis is the battery voltage in Volts and the y-axis is the crankshaft rotation speed in revolutions per minute.

[0059] Five points XI, X2, VI, V2, T are placed on the graph, whose coordinates are:

[0060] • XI: 7.5 V; 71 rpm

[0061] • X2: 9.6 V; 98 rpm

[0062] • VI: 6.9 V; 52 rpm

[0063] • V2: 9.5 V; 78 rpm

[0064] • T: 8.5 V; 95 rpm.

[0065] Points VI and V2 are points where the first tooth is not missed while points XI and X2 are points where the tooth is missed.

[0066] Experience shows that the set of points for which the first tooth is not missed can be separated by a straight line D from the set of points for which the first tooth is missed.

[0067] Thus, given a battery voltage value at crankshaft startup, the line defines a predetermined threshold value for said battery voltage value.

[0068] We can thus understand that point T corresponds to a first missed tooth. In fact, the first determined rotation speed of 95 rpm is higher than the predetermined threshold value for a voltage of 8.5 which is approximately 85 rpm.

[0069] The module M according to the invention can be implemented in the form of an electronic module comprising a memory in which is stored a computer program product comprising instructions intended to be executed by the calculation unit UC or by the engine control unit ECU which then replaces the calculation unit UC.

[0070] Finally, the method according to the invention and the corresponding module can be implemented with sensors other than magnetic ones, provided that the sensor is sensitive to the passage of target reference elements.

[0071] Of course, the invention is not limited to the examples just described and many adjustments can be made to these examples without departing from the scope of the invention. In addition, the various features, forms, variants and embodiments of the invention can be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive.

Claims

Claims 1) Method for predictive maintenance (P) of a crankshaft angular position sensor (S) (A) intended to be started by a starter powered by a battery, the sensor being intended to generate a voltage signal comprising falling edges corresponding to detections of rising edges of a series of teeth of a toothed wheel mounted integral with the axis of rotation of the crankshaft, the method being implemented by a calculation unit (Uc) configured to detect a falling edge of said voltage signal, the method comprising the following steps, implemented after detection of the starting of the vehicle: / a / measure (Em) a battery voltage value, / b / determine (Ea) a first current rotation speed of the crankshaft by processing said voltage signal, / c / generate (Eg) an alarm when the first determined rotation speed is greater than a predetermined threshold value for said measured battery voltage value. 2) Method according to the preceding claim, in which step / c / of generating an alarm is implemented after a post-processing step in which it is determined whether the vehicle is started in a signature zone of the toothed wheel, the generation of an alarm being blocked if it is determined that the vehicle was started in the signature zone. 3) Method according to one of the two preceding claims, in which the calculation unit (Uc) has undergone, prior to step / a / of measuring (Em) a battery voltage value, a modeling step (Ei) in which said threshold value of the first rotation speed is determined, as a function of the battery voltage value. 4) Method according to any one of the preceding claims, in which step / c / of generating an alarm is followed by a step of replacing (Er) the crankshaft sensor (S), carried out by a human operator. 5) Method according to any one of the preceding claims, in which step / b / of acquiring the first current speed comprises: • an acquisition by the sensor at a current time, of a first rising edge, respectively falling edge, and a start of a time delay, then • an acquisition by the sensor at a second current instant of a second rising edge, respectively falling edge, and a stop of the time delay. 6) Module (M) for predictive maintenance of a magnetic sensor (S) of angular position (A) of crankshaft intended to be started by a starter powered by a battery, the sensor being intended to generate a voltage signal comprising falling edges corresponding to detections of rising edges of a series of teeth of a toothed wheel mounted integrally with the axis of rotation of the crankshaft the module comprises a calculation unit (Uc) configured to detect a falling edge of said voltage signal, and to, after detection of the starting of the vehicle: measure a voltage value of the battery when the crankshaft starts, determine a first current rotation speed of the crankshaft by processing said signal, generate an alarm when the first determined rotation speed is greater than a predetermined threshold value for said measured battery voltage value.

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