FR3144845A1 - Method for determining the rotational speed of an internal combustion engine - Google Patents

Abstract

Method for determining the rotational speed of a motor comprising the following steps: - successive storage (100) of tooth passage times (Δti), the number of stored passage times being strictly greater than the number of teeth passing in front of the sensor between a first and a second minimum rotation speed, - determination of the angular position (200) of the respective motor corresponding to the first (Pn-1) and the second minimum speed (Pn), - determination of the duration elapsed (300) between the passage of the first speed minimum and the passage of the second speed minimum, and - determination of the rotation speed (400) of the motor from the angular difference between the first rotation speed minimum and the second minimum rotation speed, on the one hand, and the durations stored between the first and the second minimum speed. Abstract Figure: Figure 5

Description

Method for determining the rotational speed of an internal combustion engine

The present disclosure relates to a method for determining the rotational speed of an internal combustion engine. It relates more particularly to a determination of the rotational speed of the engine in order to monitor a speed measurement made on the engine.

The technical field of the present invention is thus the field of engine control for an internal combustion engine. It concerns any type of internal combustion engine comprising a crankshaft with a toothed target associated with a sensor. The present disclosure is intended in particular for a motor vehicle or similar (motorcycle, truck, etc.) but can also be used for another type of vehicle (boat or other).

In an internal combustion engine, pistons slide in cylinders and rotate a flywheel through a connecting rod-crankshaft system and this movement is transmitted to the vehicle's wheels to move it. To manage the operation of the engine, an important parameter is the rotation speed of this engine which corresponds to the rotation speed of the crankshaft. This speed is measured by a "primary" measurement. For safety reasons, it is advisable to monitor the speed measurement and determine it in a manner separate from that for making the "primary" measurement. It is indeed necessary to avoid having an unexpected acceleration of the corresponding vehicle. When the vehicle's wheels are coupled to said engine by a clutch, a direct connection is established between the engine and the wheels and an unexpected variation in the engine's rotation speed will have a negative effect on the vehicle's acceleration.

Monitoring the engine speed often involves several components, such as one (or more) sensor(s) and an electronic unit such as a generic timer module (known by the English sign GTM for Generic Timer Module).

The present disclosure improves the situation. The original idea underlying the present disclosure is to attempt to determine a rotational speed of an engine solely from the signals of a sensor associated with a crankshaft target. The present disclosure then aims to provide the corresponding method. This method will preferably make it possible to obtain a reliable determination of the rotational speed, advantageously over the entire operating speed range of the engine. Advantageously, this method will be operational as soon as the engine is started, even before synchronizing the engine. Preferably, the present disclosure will provide a method making it possible to limit the computational load within a computer used for engine management, particularly when the engine rotational speed is high.

Summary

A method is proposed for determining the rotational speed of an internal combustion engine comprising a crankshaft with a target having regularly distributed teeth on its periphery, said target being associated with a sensor detecting a tooth front for each tooth.

According to the present disclosure, the proposed method comprises the following steps:
- successive storage of the passage times of teeth of the target in front of the sensor, the number of passage times stored being strictly greater than the number of teeth passing in front of the sensor between a first minimum rotation speed and a second minimum rotation speed,
- determination of an angular position deviation of the motor between the angular position corresponding to the first minimum speed and the angular position corresponding to the second minimum speed,
- determination of the time elapsed between the passage of the angular position of the motor corresponding to the first minimum speed and the passage of the angular position of the motor corresponding to the second minimum speed, and
- determination of the rotational speed of the motor from the angular difference between the angular position corresponding to the first minimum rotational speed and the angular position corresponding to the second minimum rotational speed, on the one hand, and the tooth passage times stored between the first minimum speed and the second minimum speed.

Such a method can be implemented as soon as a sensor associated with a crankshaft target is operating. Then, as soon as the dedicated buffer is filled, a rotational speed can be determined as a control speed of a measured rotational speed. In a four-cylinder engine, a speed check can be made as early as the first engine revolution, before 360°CRK, i.e. even before a synchronization is generally performed.
In this process, a tooth passage time corresponds to the time that elapses between the passage of two successive similar edges (rising or falling).

In a method as presented above, the features set forth in the following paragraphs may, optionally, be implemented, independently of one another or in combination with one another:

- the tooth passage times are stored in a buffer memory which can contain a predetermined number of data, and when the buffer memory is full, a new data corresponding to a new measured duration replaces the oldest data stored;

- the target has a singularity in the form of a hollow corresponding to i missing teeth, and when passing through said hollow the measured passage time is divided by (i+1) and (i+1) times corresponding to the result obtained by this division are stored;

- the first minimum speed and the second minimum speed correspond to two successive minimum speeds;

- from a predetermined number of stored target tooth passage times, a respective corresponding instantaneous rotation speed is determined for each time, said passage times corresponding to teeth located on either side of the position corresponding to a minimum speed, and from the calculated instantaneous speeds and the known theoretical angular positions of the corresponding teeth the angular position corresponding to a minimum of the rotation speed of the motor is determined by the least squares method;

- for determining the time elapsed between the passage of the angular position of the motor corresponding to the first minimum speed and the passage of the angular position of the motor corresponding to the second minimum speed, on the one hand, the time between the passage of the angular position of the motor corresponding to the first minimum speed and the passage of the next detected tooth front and, on the other hand, the time between the passage of the last tooth front before the passage of the angular position corresponding to the second minimum speed and the passage of the angular position corresponding to the second minimum speed, are estimated by considering that the rotation speed of the motor is constant each time between the detection of two tooth fronts of the target positioned around an angular position corresponding to a minimum speed;

- to determine the engine rotation speed from the angular difference between the angular position corresponding to the first minimum rotation speed and the angular position corresponding to the second minimum rotation speed, the calculation is carried out with the theoretical angular distance separating the first minimum speed from the second minimum rotation speed.

According to another aspect, there is provided a computer program comprising instructions for implementing a method presented above when this program is executed by a processor, in particular an electronic control unit of an internal combustion engine.

According to another aspect, there is provided a non-transitory, computer-readable recording medium on which such a program is recorded.

According to another aspect, there is provided an electronic calculator intended for the management of an internal combustion engine comprising means for the implementation of each of the steps of a method described above.

According to another aspect, there is provided a motor vehicle comprising an internal combustion engine, characterized in that it comprises an electronic management computer according to the preceding paragraph.

Brief description of the drawing

Other features, details and advantages will become apparent upon reading the detailed description below, and upon analysis of the attached drawing, in which:

Fig. 1

is an illustrative diagram of a signal provided by a sensor for determining the angular position of a motor, said signal being used for implementing a method according to the present disclosure.

Fig. 2

schematically illustrates a detail of the signal of the .

Fig. 3

is a diagram with a motor position on the abscissa and a rotation speed of said motor on the ordinate.

Fig. 4

is a diagram superimposing a detail of the signal of the with the curve of the .

Fig. 5

is an illustrative diagram of two successive speed minima.

Fig. 6

is a flowchart for implementing a method according to the present disclosure.

Fig. 7

is a very schematic view of a vehicle allowing the implementation of a method according to the present disclosure.

The present description is made in relation to an internal combustion engine, of the four-stroke type. As is known to those skilled in the art, an internal combustion engine comprises one or more cylinders, each of which has a combustion chamber. Each combustion chamber is associated with a piston that slides in a back-and-forth movement, successively passing through a top dead center, then a bottom dead center, and so on. This piston is connected by a connecting rod to a crankshaft. A target is secured to the crankshaft and then makes two turns, i.e. a rotation of 720° for a combustion cycle. This target is most often provided with teeth on its periphery. Each tooth corresponds to an adjacent hollow. The periphery of the target is then divided into 60 regularly distributed sectors, each sector comprising a tooth and an adjacent hollow. However, to create a reference R on the target, two teeth are removed. We thus have 58 teeth on the periphery of the flywheel with an angular offset of 6° between two successive teeth, except of course at the level of the reference R. These teeth are thus regularly distributed (every 6°) on the periphery of the target: not on the entire periphery but on the major part of it since two teeth are missing. illustrates a signal S provided by a position sensor arranged opposite said target.

It is further assumed here that the engine considered as a purely illustrative and non-limiting example is an engine comprising four cylinders. In this case, each of the four pistons passes its top dead center (TDC) once during a combustion cycle. Here, only the top dead center after a compression phase is considered as top dead center, i.e. the top dead center near which a fuel injection is performed. By numbering the four cylinders from 0 to 3, there are then four top dead centers TDC ₀ , TDC ₁ , TDC ₂ and TDC ₃ . The engine cycle is then subdivided into four segments Seg ₀ , Seg ₁ , Seg ₂ and Seg ₃ around each of these four top dead centers, one segment corresponding substantially to a compression and expansion phase in the cylinder considered.

There illustrates on an enlarged scale the signal S on a segment Seg_i. The figure indicates the start 2 of this segment and the end 4 of it. It is assumed here that the target is mounted on the crankshaft such that the top dead center of this segment, TDC_i, coincides with the descending flank of the nineteenth tooth after the preceding reference R. This figure also shows a time interval I which corresponds to the passage time of a few teeth before the top dead center TDC_i and after this top dead center. A passage time of a tooth corresponds to the time which separates the passage of two successive similar flanks (or edges). A descending edge corresponds to the passage of a tooth to a trough and a rising edge corresponds to the passage from a trough to a tooth. It is therefore noted that this definition (rising/descending) depends on the direction of rotation of the target. We have chosen on the to take three teeth before TDC_i and three teeth after. The passage time of a tooth i is noted Δt _i , for example Δt ₁₇ for the seventeenth tooth after the previous reference R. In a manner known to those skilled in the art, the sensor associated with the target detects with greater precision either the rising flanks (or edges) or the falling flanks. The proposes a measurement of the falling edges only and the passage time of a tooth noted Δt _i actually corresponds to the passage of tooth i and the preceding trough. A duration Δt _i corresponds to the time taken by the crankshaft to turn 6° (i.e. 6°CRK) in the chosen example (60 similar sectors on the periphery of the target).

From this duration, it is possible to determine the angular speed of the motor at the moment of passage of the tooth considered:

N_i = 1 / Δt_i(or 1 / delta ti)

with N _i in revolutions per minute

and Δt _i in seconds.

(The more general formula is Ni = 60 / (delta ti * number of sectors per turn))

On the , a diagram is shown in which the angular position P is arranged on the abscissa and the rotation speed N on the ordinate. In this diagram, the points Pt _i corresponding to each time measurement and then to the speed calculation carried out are arranged. For the abscissas, the angular position of the middle of the tooth is taken.

From the measurement/calculation points, a regression is carried out using, for example, the least squares method as in document FR3065283 (another method can validly be chosen here). We then obtain a curve C which passes through a minimum.

For example, we choose a curve C of degree 2, that is to say, it can be written in the following form:

N = aP² + bP + c

This curve then passes through a minimum for P = - b / 2a, N then being worth N _min .

It is proposed here to carry out this determination of the minimum rotation speed of the engine twice, preferably for two successive top dead centers, TDC_n-1 and TDC_n. We thus obtain the angular positions of the engine Pn-1 and Pn corresponding each time to a minimum rotation speed (relative minimum). If we then know the time that has elapsed between the passage of the engine through the angular position Pn-1 and the passage of the engine through the angular position Pn, it is possible to determine the rotation speed of the engine over the time interval considered, between Pn-1 and Pn.

During a first stage 100 ( ), it is proposed to store Δt values in a buffer memory_i (as shown on ) in sufficient number to be able to determine the successive angular positions Pn-1 and Pn of the engine when it passes through a relative minimum rotational speed. We know that between Pn-1 and Pn, in the illustrated case of a four-cylinder engine illustrated in , there are approximately 180°CRK or about thirty teeth. As can be seen from the preceding description, to determine a position Pn-1, it is appropriate to have some measurements of the passage time of a tooth before the position Pn-1 and after the position Pn. In this case given as an illustrative example, it will be possible, for example, to provide a buffer memory to store, for example, about forty (but preferably about sixty in the present case in order to always have two speed minima which are spaced 30 teeth apart) passage times of a tooth. This number is adapted according to the number of cylinders and the structure of the engine.

The Δt _i values are recorded as they are acquired in the buffer memory. When the buffer is full, the most recent measurement value replaces the oldest measurement value in the buffer.

In the case illustrated here, at the reference R, two teeth are missing. The measurement between two successive tooth fronts then corresponds to the passage of three sectors. The passage time for the two successive tooth fronts can then be considered as three time measurements. According to a preferred embodiment, at a reference on the target corresponding to n missing teeth, the passage time measured between two successive tooth fronts will be divided by (n+1) and (n+1) identical values are recorded in the buffer memory.

During a second stage 200 ( ), it is proposed to determine, from the stored values, the angular positions Pn-1 and Pn corresponding to two angular positions of the motor for which the rotation speed of the motor passes through a relative minimum.

Each position Pn-1 and Pn can be determined, for example, as explained above by deducing an instantaneous speed from each recorded tooth passage time and then using the least squares method. It is not necessary to determine an instantaneous speed for each tooth and it can be done only for a few stored times corresponding to tooth passages near the considered top dead centers. Other methods than the least squares method can of course be used, but the latter proposed here makes it possible to obtain a result with precision and without requiring complicated calculations.

A third stage 300 ( ) aims to determine the time between the passage of the motor through the first angular position (Pn-1) for which the motor has a minimum rotation speed (relative minimum) and the passage of the motor through the second angular position (Pn) for which the motor again has a minimum rotation speed (relative minimum).

This duration can be determined approximately for example by adding (in the digital example illustrated in the drawing) thirty successive stored values, the first of these values corresponding to the duration of the tooth passage including the passage through position Pn-1 (or the last of these values corresponding to the duration of the tooth passage including the passage through position Pn).

It is proposed (cf. ) to determine more precisely the time which separates the passage of the motor through the first angular position Pn-1 (corresponding to the first minimum speed of the motor) from the passage of the motor through the second angular position Pn (corresponding to the second minimum speed of the motor).

The angular position Pn-1 is known since it was determined in the previous step. This angular position Pn-1 is located in a 6° sector of the target. We assume on the that said sector corresponds to the passage time Δt _k of tooth k. For example, we assume that the corresponding sector extends between the two angular positions (6k)°CRK and (6k+6)°CRK. We then have:
6k <= Pn-1 < 6k+6

To determine the time taken by the motor to move from position Pn-1 to position (6k+6), we assume that the rotation speed of the motor during the passage of tooth k was constant. This approximation is (very) reasonable because position Pn-1 corresponds to a (relative) speed minimum and the tangent of the speed at Pn-1 is therefore zero. The speed variation is therefore small. This rotation speed thus corresponds to the angular distance (i.e. 6°) between two successive falling edges (in the chosen example) divided by the time difference between the two acquisitions corresponding to these two edges. Subsequently, the estimated time between the moment when the speed is assumed to be minimal (result of the least squares method) and the acquisition of the preceding (respectively later) tooth edge is determined by a rule of proportionality as translated in the calculations below.

We call Tfn-1 the duration of passage from the angular position 6k to Pn-1 and Tbn-1 the duration of passage from the angular position of Pn-1 to 6k+6. We then have the following formulas:

Tfn-1 = (Pn-1-6k) * Δt _k / 6

Tbn-1 = (6k+6-Pn-1) * Δt _k / 6

The same calculation is then also made for Pn. We assume that we have:

6m <= Pn < 6m+6

The duration T_mon ( ) between the passage of the motor through the angular position Pn-1 to the angular position Pn is then:

T_mon = Tbn-1 + [sum of Δtj for j varying from k+1 to m-1] + Tfn

The angular position Pn-1 corresponding to the passage through a first relative minimum of rotation speed of the motor, the angular position Pn corresponding to the passage through a second relative minimum of rotation speed of the motor, and the duration T_mon for the motor to pass from the angular position Pn-1 corresponding to the first minimum of speed to the angular position Pn corresponding to the second minimum of speed having now been determined, it is then possible to determine a control speed of the motor.

To obtain a control speed V_mon in rpm with angular positions given in degrees and durations in seconds, we will have:

V_mon = [(Pn – Pn-1) / 360] / [T_mon / 60]

Either

V_mon = (Pn – Pn-1) / (6 * T_mon)

Preferably, instead of Pn – Pn-1, we will use the theoretical angular value separating two passages through relative speed minima, that is to say the angular value to pass from one top dead center to the next top dead center, 180°CRK in the numerical example taken above and illustrated in the drawing.

This motor rotation speed V_mon can then be compared to the speed measured on the motor and illustrated by a curve C' on the .

This process described above is implemented by an electronic calculator on board a vehicle, for example a motor vehicle. This calculator can be called a management unit and is also known by the English acronym CPU. As illustrated schematically in the , we have a vehicle V powered by an engine M, said engine being electronically managed by at least one electronic unit CPU.

On this , a crankshaft target 10 has also been schematically represented. This target 10 is associated with a sensor 20 which provides a signal processed by the CPU unit with which the buffer memory 30 mentioned above is associated.

This technical solution can be applied in particular in engine control to monitor the engine rotation speed.

The proposed method, and the corresponding means for implementing this method, make it possible to provide a monitoring rotation speed regardless of the rotation speed of the engine.

The proposed method works even before engine synchronization. It is also operational even if the sensor associated with the crankshaft target should not detect a tooth on the target, or on the contrary see a tooth that does not exist on the target.

This disclosure is not limited to the proposed examples of embodiment and the variants mentioned described above, only as an example, but it encompasses all the variants that a person skilled in the art may envisage within the framework of the protection sought.

Claims (10)

Method for determining the rotational speed of an internal combustion engine comprising a crankshaft with a target (10) having regularly distributed teeth at its periphery, said target being associated with a sensor (20) detecting a tooth front for each tooth, characterized in that it comprises the following steps:
- successive storage (100) of the durations of passage of teeth (Δti) of the target in front of the sensor, the number of stored passage durations being strictly greater than the number of teeth passing in front of the sensor between a first minimum rotation speed and a second minimum rotation speed,
- determination of an angular position deviation (200) of the motor between the angular position corresponding to the first minimum speed (Pn-1) and the angular position corresponding to the second minimum speed (Pn),
- determination of the elapsed time (300) between the passage of the angular position of the motor corresponding to the first minimum speed and the passage of the angular position of the motor corresponding to the second minimum speed, and
- determination of the rotation speed (400) of the motor from the angular difference between the angular position corresponding to the first minimum rotation speed and the angular position corresponding to the second minimum rotation speed, on the one hand, and the tooth passage times stored between the first minimum speed and the second minimum speed. Method according to claim 1, characterized in that the tooth passage times are stored in a buffer memory (30) capable of containing a predetermined number of data, and in that when the buffer memory (30) is filled, a new data item corresponding to a new measured duration replaces the oldest data item stored. Method according to claim 1 or 2, characterized in that the target (10) comprises a singularity (R) in the form of a hollow corresponding to i missing teeth, and in that when passing said hollow the measured passage time is divided by (i+1) and (i+1) times corresponding to the result obtained by this division are stored. Method according to one of claims 1 to 3, characterized in that the first minimum speed and the second minimum speed correspond to two successive minimum speeds. Method according to one of claims 1 to 4, characterized in that from a predetermined number of stored target tooth passage times, a respective corresponding instantaneous rotation speed is determined for each time, said passage times corresponding to teeth located on either side of the position corresponding to a minimum speed, and in that from the calculated instantaneous speeds and the known theoretical angular positions of the corresponding teeth the angular position corresponding to a minimum of the rotation speed of the motor is determined by the least squares method. Method according to one of claims 1 to 5, characterized in that for determining the time elapsed between the passage of the angular position of the motor corresponding to the first minimum speed and the passage of the angular position of the motor corresponding to the second minimum speed, on the one hand, the time between the passage of the angular position of the motor corresponding to the first minimum speed and the passage of the next detected tooth front and, on the other hand, the time between the passage of the last tooth front before the passage of the angular position corresponding to the second minimum speed and the passage of the angular position corresponding to the second minimum speed, are estimated by considering that the rotational speed of the motor is constant each time between the detection of two tooth fronts of the target positioned around an angular position corresponding to a minimum speed. Method according to one of claims 1 to 6, characterized in that for determining the rotational speed of the engine from the angular difference between the angular position corresponding to the first minimum rotational speed and the angular position corresponding to the second minimum rotational speed, the calculation is carried out with the theoretical angular distance separating the first minimum speed from the second minimum rotational speed. Computer program comprising instructions which, when the program is executed by a computer, cause the latter to implement all the steps of a method according to one of claims 1 to 7. Electronic calculator intended for the management of an internal combustion engine, characterized in that it comprises means for the implementation of each of the steps of a method according to one of claims 1 to 7. Motor vehicle comprising an internal combustion engine, characterized in that it comprises an electronic computer according to claim 9.