Method for detecting a disconnection of one of the electrical wires of a crankshaft sensor of a piston engine and associated module

Abstract

Method for detecting disconnection of one of the electrical wires of a magnetic sensor (S) of the angular position of the crankshaft (A) of a thermal engine of a vehicle, the vehicle comprising a computer (Uc) configured to determine (Ea) a reference angular position of the crankshaft corresponding to a local minimum speed, then at a current instant: determine (Eb) a current local minimum speed from the voltage signal then a current angular position of the crankshaft corresponding to said determined current local minimum speed; determine (Ec) an angular position deviation equal to the difference between said current angular position and said reference angular position; if the absolute value of said minimum speed deviation is greater than a predetermined threshold, a generation (Eg) of an alarm of disconnection of one of said two electrical wires. Figure for the abstract: Figure 4.

Description

Title of the invention: Method for detecting a disconnection of one of the electrical wires of a crankshaft sensor of a piston engine and associated module Field of the invention

[0001] The present invention relates to the field of maintenance of parts associated with a piston thermal engine. It relates in particular to the detection of a disconnection of one of the electrical wires of a crankshaft sensor of such an engine and associated module. Prior art

[0002] The cycle of an internal combustion engine comprises several phases whose occurrence is offset in time for each cylinder, the synchronized control of the valves of the thermal engine being carried out by the camshaft.

[0003] 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.

[0004] The camshaft is rotated by the crankshaft. The crankshaft is a mechanical device which, by means of a connecting rod, allows the transformation of 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.

[0005] Thus, knowledge of 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.

[0006] Such a reference is available via a toothed wheel, also called a target, integral in rotation with the crankshaft. The wheel is associated with a dedicated sensor, called a crankshaft sensor, whose role ultimately is to allow the determination of the angular position and the rotational speed of the toothed wheel. The sensor is equipped with a sensitive element. According to 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 distributed around its periphery. The function of the crankshaft sensor is to transform the measured magnetic field into an electrical signal and thus to provide a potential signal on two wires connected to it. The crankshaft sensor is typically mounted near the flywheel which serves as a rotating target or supports such a target.

[0007] The rotating target has a signature, also called a long tooth or gap, formed by a singularity in the profile (otherwise regular) usually corresponding to two missing marks, and which makes it possible to fix a reference for the position of the crankshaft. 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.

[0008] A commonly used rotating target includes 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 (34 marks plus two missing marks).

[0009] 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 which can subsequently be sent to the engine management computer by means of electrical wires. The voltage variations comprise rising edges and falling edges forming a periodic signal synchronized with the passage of the markers in front of the sensor.

[0010] From the voltage data received by means of the electrical wires, 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.

[0011] The sensor is passive and comprises two wires which each transmit information from the target and which are slightly out of phase with each other.

[0012] However, it happens that one of the two electrical wires is disconnected.

[0013] When only one of the two electrical wires is disconnected, the voltage signal used to determine the position of the motor is similar to the normal signal (same general form). It is therefore difficult to detect the break in one of the two wires.

[0014] There is a method for detecting a disconnected wire, but it does not work at low speed. In addition, the method requires calibration which is not easy and can lead to cases of false detection of wire disconnection.

[0015] An aim of the invention is to propose a method for detecting a disconnection of one of the electrical wires of a crankshaft sensor of a piston engine and associated module which overcomes the drawbacks of the state of the art. Statement of the invention

[0016] To this end, there is proposed, according to a first aspect of the invention, a method for detecting disconnection of one of the two electrical wires of a magnetic crankshaft angular position sensor of a thermal engine of a vehicle,

[0017] the magnetic sensor being provided to generate a voltage signal whose envelope has an amplitude which varies with the rotation speed of said crankshaft associated with said sensor within said thermal engine,

[0018] said vehicle comprising a computer configured to: • determine a reference angular position of the crankshaft corresponding to a local minimum speed from the voltage signal, • then at a current time: • determine a current local minimum speed from the voltage signal then a current angular position of the crankshaft corresponding to said determined current local minimum speed, • determine an angular position deviation equal to the difference between said current angular position and said reference angular position, • if the absolute value of said minimum speed deviation is greater than a predetermined threshold, generation of a disconnection alarm of one of said two electrical wires.

[0019] The method may comprise an assignment of the value of said current angular position to the value of said reference position, when the absolute value of said minimum speed deviation is less than a predetermined threshold.

[0020] Advantageously, the step of generating a disconnection alarm for one of said two electrical wires further comprises determining the disconnected electrical wire from the sign of said angular position difference.

[0021] Preferably, the method further comprises a determination of a current position from an acquisition of a current rotation speed of the crankshaft from the voltage signal then a correction of the position thus determined from said angular position deviation.

[0022] According to a second aspect of the invention, there is proposed a module for disconnecting one of the two electrical wires of a magnetic sensor for the angular position of the crankshaft of a thermal engine of a vehicle, the magnetic sensor being provided to generate a voltage signal whose envelope has an amplitude which varies with the rotation speed of said crankshaft associated with said sensor within a thermal engine, the vehicle comprising a computer configured to: • determine a reference angular position of the crankshaft corresponding to a local minimum speed, • then at a current time: • determine a current local minimum speed from the voltage signal then a current angular position of the crankshaft corresponding to said determined current local minimum speed, • determine an angular position deviation equal to the difference between said current angular position and said reference angular position, • if the absolute value of said minimum speed deviation is greater than a predetermined threshold, generation (Eg) of a disconnection alarm of one of said two electrical wires. Brief description of the figures

[0023] 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: • [Fig. 1] illustrates an embodiment of a module according to the invention and its physical environment, • [Fig.2] includes a graph of the evolution of the rotation speed of a heat engine and a graph of a voltage signal generated by a magnetic sensor, • [Fig.3] includes graphs of the time evolution in voltage of signals processed by a control unit, and • [Fig.4] illustrates an embodiment of a method according to the invention. Detailed description of the invention

[0024] 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.

[0025] There is now described, with reference to [Fig.l], an embodiment of a method P for predictive maintenance of a magnetic sensor S of the angular position of the crankshaft A of a thermal engine of a vehicle implemented by the computer Uc, at the same time as a module M implementing the computer Uc. The computer Uc can receive information from an engine control unit ECU, or provide it with information.

[0026] The magnetic sensor S is designed to generate a voltage signal whose envelope E has an amplitude which varies with the rotation speed of the crankshaft A associated with the sensor within the thermal engine (see [Fig.2] below). The magnetic sensor S is typically associated with a magnetic target C mounted integral with the rotation of the crankshaft A.

[0027] More precisely, two electrical wires are connected to two terminals, called + terminals and - terminals, of the sensor. The voltage signal is equal to the potential difference between the + and - terminals.

[0028] [Fig.2] illustrates an example of a graph G1 of the evolution of the rotation speed of the thermal engine as a function of time and a graph G2 of a voltage signal generated at the same times by a magnetic sensor, said voltage signal being an alternating signal whose amplitude is delimited by an envelope E.

[0029] [Fig.3] comprises in the upper part two CRK, CRK+ graphs each presenting a first time period of 4 milliseconds of sinusoidal shape presenting a first amplitude corresponding to 250 revolutions per minute and a second time period of 2 milliseconds of sinusoidal shape corresponding to 500 revolutions per minute.

[0030] One of the two CRK graphs corresponds to the time evolution in voltage of said voltage signal and has a zero average voltage. The other of the two CRK+ graphs corresponds to the time evolution in voltage of the signal coming from the + terminal and has a voltage substantially equal to 2 Volts.

[0031] The CRK signal is the signal normally received by the ECU, which corresponds to a crenellated signal C after processing by the ECU shown in the lower part of the figure.

[0032] When the wire that is supposed to be connected to terminal - is no longer connected to said terminal -, the signal actually received by the ECU is in fact the CRK+ signal. The C+ crenellated signal after processing by the ECU is also shown in the lower part of the figure.

[0033] In a known manner, the calculator Uc is configured to determine an angular position of the crankshaft from said voltage signal.

[0034] As can be seen, it is difficult to distinguish the C and C+ signals in the absence of a time reference.

[0035] The method P according to the invention comprises a step Ea of determination by the computer Uc of a reference angular position of the crankshaft corresponding to a local minimum speed.

[0036] The determination of a reference angular position of the crankshaft corresponding to a local minimum speed is known to those skilled in the art and the reader may advantageously refer to publication WO2002245080.

[0037] This determination consists of generating a speed curve in the vicinity of the top dead centers of combustion of each of the cylinders and approximating this curve by a parabola obtained by the mathematical method of least squares. Knowing the minimum of the parabola which corresponds to the minimum speed of the crankshaft, the The angular position of the crankshaft corresponding to the minimum speed is then determined.

[0038] An idea which is at the origin of the invention consists in noting that the angular position of the minimum speed of the crankshaft hardly changes, neither with time, nor with the engine speed. Consequently, detection by the computer of a sudden change in the angular position of the minimum speed indicates a failure of the measurement and thus the disconnection of one of the two electrical wires of the sensor.

[0039] Also, the method P according to the invention comprises, after carrying out step Ea: • a step Eb of determining a current local minimum speed from the voltage signal then from a current angular position of the crankshaft corresponding to said determined current local minimum speed, • a step Ec of determining an angular position deviation equal to the difference between said current angular position and said reference angular position, • if the absolute value of said minimum speed deviation is greater than a predetermined threshold, a generation Eg of a disconnection alarm of one of said two electrical wires.

[0040] The current local minimum speed designates the minimum rotational speed of the crankshaft near the top dead center of each combustion.

[0041] Optionally, the method may comprise an assignment Ef of the value of said current angular position to the value of said reference angular position when the absolute value of said minimum speed deviation is less than a predetermined threshold.

[0042] Preferably, the step Eg of generating an alarm for disconnection of one of said two electrical wires further comprises determining the disconnected electrical wire from the sign of said angular position difference.

[0043] When the angular position deviation is negative, the determined electrical wire is the wire connected to the - terminal. When the angular position deviation is positive, the determined electrical wire is the wire connected to the + terminal.

[0044] Subsequently, a determination of an angular position by the computer from the voltage signal can advantageously be corrected from the angular position deviation, which makes it possible to synchronize the valves while a wire is disconnected.

[0045] 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 UC computer or by the engine control unit ECU which then replaces the UC computer.

[0046] 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 reference elements of the target.

[0047] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention. In addition, the various characteristics, forms, variants and embodiments of the invention can be associated with each other in various combinations to the extent that they are not incompatible or exclusive of each other.

Claims

Claims

1. Method for detecting disconnection of one of the two electrical wires of a magnetic sensor (S) of the angular position of the crankshaft (A) of a thermal engine of a vehicle, the magnetic sensor being provided to generate a voltage signal whose envelope (E) has an amplitude which varies with the rotation speed of said crankshaft (A) associated with said sensor within said thermal engine, said vehicle comprising a computer (Uc) configured to: determine (Ea) a reference angular position of the crankshaft corresponding to a local minimum speed from the voltage signal, then at a current instant: determine (Eb) a current local minimum speed from the voltage signal then a current angular position of the crankshaft corresponding to said determined current local minimum speed,determining (Ec) an angular position deviation equal to the difference between said current angular position and said reference angular position, if the absolute value of said minimum speed deviation is greater than a predetermined threshold, a generation (Eg) of a disconnection alarm of one of said two electrical wires, the step of generating (Eg) a disconnection alarm of one of said two electrical wires further comprising a determination of the disconnected electrical wire from the sign of said angular position deviation.,

2. Method according to claim 1, comprising an assignment (Ef) of the value of said current angular position to the value of said reference position, when the absolute value of said minimum speed deviation is less than a predetermined threshold.

3. Method according to any one of the preceding claims, comprising a determination of a current position from an acquisition of a current rotation speed of the crankshaft (A) from the voltage signal then a correction of the position thus determined from said angular position difference.

4. Module (M) for detecting the disconnection of one of the two electrical wires of a magnetic sensor (S) of the angular position (A) of the crankshaft of a thermal engine of a vehicle, the magnetic sensor being designed to generate a voltage signal whose envelope (E) has an amplitude which varies with the rotation speed of said crankshaft (A) associated with said sensor within a heat engine, the module (M) comprising a calculator (Uc) configured to: determine (Ea) a reference angular position of the crankshaft corresponding to a local minimum speed, then at a current time: determine (Eb) a current local minimum speed from the voltage signal then a current angular position of the crankshaft corresponding to said determined current local minimum speed, determine (Ec) an angular position deviation equal to the difference between said current angular position and said reference angular position, if the absolute value of said minimum speed deviation is greater than a predetermined threshold, a generation (Eg) of a disconnection alarm of one of said two electrical wires, the generation (Eg) of a disconnection alarm of one of said two electrical wires further comprises a determination of the disconnected electrical wire from the sign of said angular position deviation.

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