FR3101375A1 - REVERSIBLE CAMSHAFT TARGET - Google Patents

Abstract

The present application relates to a camshaft toothed wheel (2, 2a, 2b), forming a target for a camshaft position sensor (1), comprising a circular body provided with two opposite main faces and being provided on its circumference of a series of 6 teeth minimum and 7 teeth maximum, for which the series of teeth comprises, in a first direction of rotation (3) given of the wheel, four teeth (4, 5, 7, 9) of which the Rising edges spaced 180 ° apart CRK constitute reference edges for determining the rotational position of a 4 cylinder engine, for which the falling edge of a first of these teeth constitutes, with two falling edges of two additional teeth (6, 8), the reference edges spaced at 240 ° CRK to determine the rotational position of a 3-cylinder engine and for which the angular distance between two teeth is greater than or equal to Arctan (4 / (R + h)) ° CAM and the angular width of a tooth is greater than or equal to Arctan (2,5 / (R + h)) ° CAM o ù R is the radius of the wheel excluding teeth and h is the height of the tooth expressed in mm. The invention applies to an engine control system comprising a computer, a crankshaft target and a camshaft target. Figure 1

Description

REVERSIBLE CAMSHAFT TARGET

The present application relates to a reversible camshaft target intended to be compatible with 3 or 4 cylinder four-stroke engines of small size such as two or three-wheel vehicle engines, for example motorcycle or scooter engines.

In the operating cycle of a four-stroke internal combustion engine, it is necessary to know precisely the position of the crankshaft in order to be able to synchronize different actions such as fuel injection, spark plug control, distribution bodies, etc. This optimizes combustion efficiency and reduces fuel consumption and harmful emissions. In other words, an internal combustion engine must be synchronized (phased) in order to determine and optimize the best moment to burn the fuel in the cylinder with a view to optimizing emissions, consumption, etc….

Synchronization or phasing is generally achieved by combining information from a crankshaft position sensor and a camshaft position sensor which detect targets such as teeth on sprockets.

To do this, a crankshaft conventionally comprises a toothed wheel, or crankshaft target, which typically comprises a set of teeth regularly distributed along its circumference (for example from 36 to 120 teeth), and whose teeth are detected by a sensor called CRK sensor. The toothed wheel integral with the crankshaft comprises a reference portion devoid of teeth in the form of a hollow or a long tooth, also called GAP term used below. By detecting the passage of the teeth in front of the sensor and counting the number of teeth counted from the gap during engine rotation, it is possible to know the position of the crankshaft over a 360° crankshaft revolution, in other words 360°CRK angle of rotation of the crankshaft being expressed in °CRK.

The crankshaft target provided with teeth, thus presents an asymmetry generally called signature produced by the mark which makes it possible to know the engine position to within 360°.

However, one engine cycle corresponds to two complete rotations of the crankshaft, and knowledge of the angular position of the crankshaft is therefore insufficient to determine the position of the engine.

This information is therefore combined with information on the angular position of the camshaft, which is rotated by the crankshaft, and which also includes a toothed wheel whose teeth are detected by a corresponding sensor.

While one engine cycle corresponds to two 360° rotations of the crankshaft, it only corresponds to one 360° rotation of the camshaft or 360°CAM, the angle of rotation of the camshaft being expressed in °CAM. Consequently, the gear wheel of the camshaft has a rotational asymmetry which, combined with the information on the position of the crankshaft, makes it possible to accurately deduce the state of the engine cycle. The additional information from the camshaft (with its revolution of 360°CAM equal to 720°CRK), makes it possible to determine correct phasing, that is to say, makes it possible to know with certainty where each cylinder in the combustion cycle.

The succession of signals received by the camshaft sensor called CAM is not regular, but follows a known profile which allows more precise knowledge of the position of the cylinders in the engine.

The synchronization method consists, at each gap, in comparing the information received by the camshaft sensor with theoretical information stored in the computer. If this information is similar, the gap is recognized, and the engine position as well.

Thus, each time the engine is started, the engine is synchronized when the crankshaft gap combined with the detection of the condition of the camshaft wheel is detected.

In order to reduce fuel consumption as well as emissions, Variable Valve Timing (VVT) technology in which the angular position of the shaft is varied at intake cams and/or the exhaust camshaft to cause recirculation of the exhaust gases in the cylinders is increasingly employed.

To control these systems, a gear-type target at the end of the camshaft is used (called the CAM target) which comprises an arrangement of teeth making it possible to know the angle of the crankshaft, and therefore the position of the pistons in the cylinders in the engine cycle.

For CAM sensors associated with CAM targets, two technologies exist, namely:

1. TPO “True Power On” sensors which are sensors suitable for detecting high or low levels corresponding respectively to dips and teeth on the gear wheel. These sensors have an average precision in the detection of a passage between a hollow and a tooth or a passage between a tooth and a hollow but allow a faster synchronization of the motor because they can be used with targets equipped with teeth of different widths (width is the distance between a rising edge and a falling edge of a tooth) and allow these teeth to be recognized, which allows an average synchronization distance of 230°CRK.

2. Differential sensors. These sensors are not able to read the level of the teeth or valleys of a CAM target but detect the rising edges between a valley and a tooth or the falling edges between a tooth and a valley. These sensors have greater temporal precision (detection on edge) but have a lower average synchronization speed than TPO sensors with current target designs on average 280°CRK because they do not allow to know the width of the teeth as well as their high or low levels.

1. un premier groupe comporte une dent,
2. un deuxième groupe comporte deux dents,
3. un troisième groupe comporte trois dents, et
4. un quatrième groupe comporte quatre dents,

les groupes de dents étant agencés de sorte que :Application FR18 55382 filed on 06/19/2018 describes a camshaft toothed wheel, comprising a plurality of teeth distributed over its circumference, the toothed wheel comprising four groups of teeth such as:

1. a first group comprises a tooth,
2. a second group has two teeth,
3. a third group has three teeth, and
4. a fourth group has four teeth,

the groups of teeth being arranged so that:

the consecutive teeth of each group comprising at least two teeth are all spaced apart by the same angular distance,

the toothed wheel comprises, between two consecutive groups of teeth, a toothless portion extending over at least 35°CAM,

there are four teeth spaced 90°CAM on the circumference of the sprocket, and three teeth spaced 120°CAM on the circumference of the sprocket.

Such a toothed wheel for a traditional motor vehicle engine measures around 50 mm in diameter and is well suited to motor vehicle engines with 3 or 4 cylinders. However, it is not suitable for small-sized engines such as two- or three-wheel vehicle engines whose diameter of the CAM targets generally does not exceed 40mm because the rocker cover(s) are of small size.

Technical problem

Such a target is not suitable for a wheel with a smaller diameter because the distance between the fronts would no longer be large enough to discriminate between these fronts.

Furthermore, it is desirable for manufacturers of two-wheel engines to reduce the number of target references in their range of engines and in particular to be able to use the same target for three- or four-cylinder engines would be a significant economic advantage.

In this context, the present application proposes a reversible reduced-diameter camshaft target compatible with 3 or 4-cylinder engines of small dimensions, in particular motorcycle engines.

More specifically, the present application relates to a camshaft toothed wheel, forming a target for a camshaft position sensor, comprising a circular body provided with two opposite main faces and being provided on its circumference with a series of teeth, for which said series of teeth comprises a minimum of six teeth and a maximum of seven teeth divided into three groups, for which in a given first direction of rotation of the wheel, four teeth of said series, the rising edges of which are spaced apart by 90°CAM, i.e. 180 °CRK constitute reference edges for determining the rotational position of a 4-cylinder engine, for which the falling edge of a first of these four teeth constitutes, with two falling edges of two additional teeth of the said series, the edges of reference spaced 120°CAM or 240°CRK to determine the rotational position of a 3-cylinder engine and for which the angular distance between two teeth is greater than or equal to Arctan(4/(R+h))°CAM and the angular width of a tooth is greater than or equal to Arctan(2.5/(R+h))°CAM where R is the radius of the wheel excluding teeth and h is the height of the tooth expressed in mm.

In addition to the fact that it is suitable for small diameters of toothed wheels, the target of the present application has the advantage of being reversible, that is to say that in a second direction of reverse rotation, the rising edges become the edges used to determine the rotational position of a 3-cylinder engine and the falling edges constitute reference edges to determine the rotational position of a 4-cylinder engine

With traditional sensors of the differential type, a width of 4 mm between the teeth is the minimum distance to discriminate the existence of two successive fronts and a width of the upper part of the teeth of 2.5 mm being the minimum distance to form a tooth which carries a front, while the height of the teeth is of the order of 4 mm to 5 mm.

In this way, the teeth have sufficient height and width to detect their rising edges or their falling edges depending on the sensor.

Preferably, the teeth of the series of teeth are grouped together according to three groups of teeth successively provided with one, two and four teeth or with one, four and two teeth.

This configuration makes it possible to have a reduced number of teeth while simplifying the detection of the sequence of teeth of the wheel.

Advantageously, for a wheel with an outside diameter of 40mm with standard automotive tolerances, the minimum angular distance between two identical fronts is greater than or equal to Arctan(4/(R+h)) + Arctan(2.5/(R +h)) or rounding up: 18.5°CAM or 37°CRK with R radius of the wheel excluding teeth of 15 mm and h height of the tooth of 5 mm.

This allows detection of gaps between teeth.

According to an advantageous embodiment of the invention, the teeth are of identical angular width.

In this way the synchronization calculation is simplified.

1. le premier groupe de dents comporte une dent isolée dont le front montant correspond à un angle 0° moteur quatre cylindres et le front descendant correspond à un angle 0° moteur trois cylindres ;
2. le deuxième groupe de dents comporte deux dents telles que le front montant de la première desdites deux dents correspond à un angle de 180° CRK moteur quatre cylindres et le front descendant de la seconde desdites deux dents correspond à un angle de 240° CRK moteur trois cylindres ;
3. le troisième groupe de dents comporte quatre dents à égale distance angulaire les unes des autres telles que le front montant de la première desdites quatre dents correspond à un angle de 360° CRK moteur quatre cylindres, la deuxième desdites quatre dents est une dent de synchronisation pourvue d’un front montant à 420°CRK et un front descendant à 440°CRK, le front descendant de la troisième desdites quatre dents correspond à un angle de 480° CRK moteur trois cylindres et le front montant de la dernière desdites quatre dents correspond à un angle de 540° CRK moteur quatre cylindres.

According to a first embodiment for which a synchronization tooth is present, in said first direction of rotation:

1. the first group of teeth comprises an isolated tooth whose rising edge corresponds to a 0° angle with a four-cylinder engine and the falling edge corresponds to a 0° angle with a three-cylinder engine;
2. the second group of teeth comprises two teeth such that the rising edge of the first of said two teeth corresponds to an angle of 180° CRK with a four-cylinder engine and the falling edge of the second of said two teeth corresponds to an angle of 240° CRK with a three-cylinder engine cylinders;
3. the third group of teeth comprises four teeth at equal angular distance from each other such that the rising edge of the first of said four teeth corresponds to an angle of 360° CRK four-cylinder engine, the second of said four teeth is a synchronization tooth provided of a rising edge at 420°CRK and a falling edge at 440°CRK, the falling edge of the third of said four teeth corresponds to an angle of 480° CRK with a three-cylinder engine and the rising edge of the last of said four teeth corresponds to a 540° angle CRK four-cylinder engine.

1. le premier groupe de dents comporte une dent isolée dont le front montant correspond à un angle 0° moteur quatre cylindres et le front descendant correspond à un angle 0° moteur trois cylindres ;
2. le deuxième groupe de dents comporte quatre dents à égale distance angulaire les unes des autres telles que le front montant de la première desdites quatre dents correspond à un angle de 180° CRK moteur quatre cylindres, le front descendant de la deuxième desdites quatre dents correspond à un angle de 240° CRK moteur trois cylindres la troisième desdites quatre dents est une dent de synchronisation pourvue d’un front montant à 300°CRK et un front descendant à 320°CRK et le front montant de la quatrième desdites quatre dents correspond à un angle de 360° CRK moteur quatre cylindres ;
3. le troisième groupe de dents comporte deux dents telles que le front descendant de la première desdites deux dents correspond à un angle de 480° CRK moteur trois cylindres et le front montant de la seconde desdites deux dents correspond à un angle de 540° CRK moteur quatre cylindres.

According to a second embodiment for which a synchronization tooth is present, the toothed wheel is such that in said first direction of rotation:

1. the first group of teeth comprises an isolated tooth whose rising edge corresponds to a 0° angle with a four-cylinder engine and the falling edge corresponds to a 0° angle with a three-cylinder engine;
2. the second group of teeth comprises four teeth at equal angular distance from each other such that the rising edge of the first of said four teeth corresponds to an angle of 180° CRK four-cylinder engine, the falling edge of the second of said four teeth corresponds to an angle of 240° CRK three-cylinder engine the third of said four teeth is a synchronization tooth provided with a rising edge at 300°CRK and a falling edge at 320°CRK and the rising edge of the fourth of said four teeth corresponds to a 360° angle CRK four-cylinder engine;
3. the third group of teeth comprises two teeth such that the falling edge of the first of said two teeth corresponds to an angle of 480° CRK with a three-cylinder engine and the rising edge of the second of said two teeth corresponds to an angle of 540° CRK with a four-cylinder engine cylinders.

The three groups of teeth of these two embodiments are easily differentiated and the synchronization of the motor is facilitated by the added synchronization tooth.

The angular width of the teeth is advantageously 10°CAM or 20°CRK and the reference falling edges at 120°CAM or 240°CRK of the three-cylinder engine position in the first direction of rotation are offset by at least Arctan(2.5 /(R+h))°CAM and preferably +10°CAM or +20°CRK with respect to the rising edges of the corresponding teeth.

The invention further relates to an engine control system comprising a computer, a crankshaft toothed wheel and a crankshaft sensor, a camshaft toothed wheel according to the invention and a differential type camshaft sensor, for which the crankshaft sprocket and the camshaft sprocket are angularly keyed so that the crankshaft sprocket has a mark (gap) wedged in a toothless space of the camshaft sprocket and for which the computer includes a engine synchronization algorithm adapted to recognize the sequences formed by the groups of teeth of the camshaft toothed wheel and to deduce the engine position in real time.

The differential camshaft sensor of the system being chosen to detect the rising edges, the toothed wheel is, according to a first embodiment, mounted in said first direction to detect the edges at 180° CRK for a four-cylinder engine and is mounted in the opposite direction to the first direction to detect fronts at 240° CRK for a three-cylinder engine.

The differential camshaft sensor of the system being chosen to detect the falling edges, the toothed wheel is, according to a second embodiment, mounted in said first direction to detect the edges at 240° CRK for a three-cylinder engine and is mounted in the opposite direction to the first direction to detect edges at 180° CRK for a four-cylinder engine.

Other characteristics, details and advantages of the invention will appear on reading the detailed description below, and on analyzing the appended drawings which describe non-limiting embodiment examples useful for understanding the invention and on which :

shows a schematic view of a camshaft sprocket according to a first embodiment of the invention;

shows a schematic view of a camshaft sprocket according to a second embodiment;

shows a timing diagram of the toothed wheel of Figure 2;

shows a timing diagram illustrating a camshaft sprocket/crankshaft sprocket synchronization according to the embodiment of FIG. 2;

shows a schematic view of a camshaft sprocket according to a third embodiment;

shows a timing diagram of the toothed wheel of Figure 5;

shows a schematic view of a demand system.

Hereinafter, it is preferable to note the angles measured in degrees CRK with respect to an angular position on a crankshaft toothed wheel since the engine control initially locks onto the crankshaft. The angular position of the camshaft sprocket in "°CAM" will be half of the angular position expressed in °CRK since a rotation of one degree CAM corresponds to a rotation of two degrees CRK.

The present invention makes it possible in particular to produce wheels with a reduced diameter of 30 mm excluding teeth with teeth of a height of 4 mm to 5 mm but also conventional wheels of 40 mm in diameter and 5 mm in height of teeth.

1. - Respecter l'espacement des fronts CAM de 90°CAM soit 180°CRK pour le contrôle de la VVT de moteurs à 4 cylindres et des fronts CAM de 120°CAM soit 240°CRK pour le contrôle de la VVT de moteurs à 3 cylindres ;
2. - Pouvoir détecter tous les fronts : pour ce faire, avec des capteurs usuels, le creux entre deux dents doit mesurer au moins 4mm et l'angle du creux pour une roue ou cible de 30mm de diamètre hors dents doit donc être supérieur à Arctan(4/(R+h)) en degrés CAM où R est le rayon de la roue hors dents exprimé en mm, de l’ordre de 15 mm, et h est la hauteur d’une dent de l’ordre de 4 mm à 5 mm ;
3. - Pouvoir détecter tous les niveaux hauts avec des capteurs usuels : la dent doit mesurer 2.5mm de large et l'angle de la dent pour une cible de diamètre extérieur 40mm doit donc être supérieur à Arctan(2,5/(R+h)) en degrés CAM où h est la hauteur d’une dent de l’ordre de 4 mm à 5 mm et R est le rayon de la roue hors dents exprimé en mm, de l’ordre de 15 mm ;
4. - Créer une asymétrie de dents la plus franche possible ;
5. - Positionner l'asymétrie du CAM en face d'un GAP.

To do this, at least some of the following constraints must be taken into account for the position of the CAM edges:

1. - Respect the spacing of the CAM fronts of 90°CAM or 180°CRK for the control of the VVT of 4-cylinder engines and the CAM fronts of 120°CAM or 240°CRK for the control of the VVT of 3-cylinder engines ;
2. - To be able to detect all the edges: to do this, with usual sensors, the hollow between two teeth must measure at least 4mm and the angle of the hollow for a wheel or target of 30mm in diameter excluding teeth must therefore be greater than Arctan( 4/(R+h)) in degrees CAM where R is the radius of the wheel excluding teeth expressed in mm, of the order of 15 mm, and h is the height of a tooth of the order of 4 mm at 5mm;
3. - Be able to detect all high levels with usual sensors: the tooth must be 2.5mm wide and the angle of the tooth for a target with an external diameter of 40mm must therefore be greater than Arctan (2.5/(R+h) ) in degrees CAM where h is the height of a tooth of the order of 4 mm to 5 mm and R is the radius of the wheel excluding teeth expressed in mm, of the order of 15 mm;
4. - Create the clearest possible tooth asymmetry;
5. - Position the asymmetry of the CAM in front of a GAP.

To respect the spacing of the rising edges CAM of 90° CAM which corresponds to 180°CRK for the control of the VVT of 4-cylinder engines, the corresponding edges on the camshaft wheel must therefore at least be positioned according to the angular position [0; 90; 180; 270] in degrees CAM i.e. [0; 180; 360; 540] in degrees CRK since 1° CAM=2°CRK.

Considering these first edges to be rising edges, if A represents the angle between the reference and the first falling edge, so that they can be seen as rising edges if the target is mounted upside down, the falling edges for control of the VVT of a three-cylinder engine must be positioned according to the angular position [A; 240+A; 480+A] in degrees CRK when the wheel is in the same orientation on the camshaft.

According to an embodiment represented in FIG. 1, which schematically represents a toothed wheel CAM 2 according to a simplified embodiment of the invention where the angles are expressed in °CRK, i.e. from 0°CRK to 720°CRK on the circumference of 360° CAM of the wheel, we choose A = 20° CRK so that the first tooth coincides with the two previous criteria, then we complete the rising and falling edges to materialize teeth of 20° CRK.

The additional rising edges are placed 20°CRK before the falling edges and the additional falling edges are placed 20°CRK after the rising edges.

This toothed wheel has six teeth 4, 5, 6, 7, 8, 9 which define four fronts at 180°CRK for a four-cylinder engine and three fronts at 240°CRK for a three-cylinder engine.

According to this example, in a first given direction of rotation of the wheel, the rising edges spaced 180°CRK from the four teeth 4, 5, 7 and 9 constitute the reference edges to determine the rotational position of a 4-cylinder engine. The falling edges of the three teeth 4, 6 and 8 constitute the reference edges spaced 240°CRK to determine the rotational position of a 3-cylinder engine. According to this configuration, the angular distance between two teeth is greater than or equal to Arctan(4/(R+h))°CAM and the angular width of a tooth is greater than or equal to Arctan(2.5/(R+h) )) °CAM where R is the radius of the wheel excluding teeth and h is the height of the tooth expressed in mm.

The rising and falling edges corresponding to the teeth defining the representative angles of 3 or 4 cylinder engines determined over a sample of time are then the following expressed in °CAM:

[0; 10; 90; 100; 120; 130; 180; 190; 240; 250; 270; 280]

Which gives in °CRK:

[0; 20; 180; 200; 240; 260; 360; 380; 480; 500; 540; 560].

To be able to synchronize the motor, it is necessary to make it possible to distinguish the edges from each other and the solution is to add at least one tooth. This tooth must be located in a free space of at least 100°CRK because it is necessary to be able to place two hollows of 40°CRK and a tooth of 20°CRK. The tooth can then be placed arbitrarily in all available recesses [20/180], [260/360], [380/480] or [560/720] expressed in °CRK.

However, the determination of the number of teeth by the injection and/or ignition computer uses the method of ratios, i.e. the times between the teeth are memorized then used to calculate a ratio of duration of tooth compared to a theoretical tooth distance ratio. Thus, to have the most different possible ratios, and thus increase the robustness of the algorithm for determining the numbers of edges, the asymmetry of the target must be as clear as possible and it is therefore better to group the teeth in bundles.

The additional tooth will therefore advantageously be placed in the interval [260/360] or [380/480] expressed in °CRK in order to make 1/4/2 or 1/2/4 packages.

According to the embodiment of Figure 2, the toothed wheel 2a, which rotates in front of a sensor 1, for example in a first direction of rotation 3, thus comprises three groups of teeth 10, 20, 30. The first group comprises a single tooth 11, the second group has two teeth 21, 22 and the third group has four teeth 31, 32, 33, 34.

The rising edges of teeth 11, 21, 31, 34 constitute marks spaced 180° CRK (i.e. 90° CAM) and the falling edges of teeth 11, 22, 33 constitute marks spaced 240° CRK (i.e. 120° CAM ).

The example of figures 2 and 3 shows tooth 32 placed in the interval [380/480] which makes packets (short intervals compared to long intervals) of type 1/2/4.

The edges determined on the time sample 40 shown in Figure 3 are then the following expressed in °CRK:

[0; 20; 180; 200; 240; 260; 360; 380; 420; 440; 480; 500; 540; 560]

This target is always symmetrical and makes it possible to have a minimum of 40°CRK between the falling edges 61, 62, 63 and rising edges 51, 52, 53, 54.

To synchronize the engine, it is necessary to use the crankshaft wheel 70 and the camshaft wheel and know their phase shift.

FIG. 7 schematically represents a system of the invention with a crankshaft wheel 70 facing a crankshaft sensor 71, a camshaft wheel 2 facing its sensor 1, the two sensors being connected to an engine computer 100 comprising an algorithm 110 of engine synchronization adapted to determine the engine phasing from the signals from the crankshaft and camshaft sensors.

The crankshaft wheel sequence is shown schematically on the timing diagram 80 in Figure 4 which shows two crankshaft revolutions with the top dead centers (TDC) of a four-cylinder engine.

An important point is to have two opposite zones of 35°CAM, i.e. 70°CRK, devoid of teeth in order to be able to place the crankshaft GAPs there.

By wedging the camshaft wheel with respect to the gap 81 between the series of teeth 82 to place it in the spaces devoid of teeth, one obtains in line 91 the rising edges of the camshaft wheel positioned in a first direction of rotation on its axis to provide the phasing of a four-cylinder engine set at 180°CRK and in line 92 the rising edges of the camshaft wheel turned over on its axis, the wheel then rotating in a second direction of reverse rotation from the first (or by flipping the sensor) to provide the phasing of a three-cylinder engine stalled at 240°CRK.

Such a solution makes it possible to solve the problems posed by the known solutions and to produce a target of smaller diameter, up to at least 40mm, compatible with 3 or 4 cylinder engines and supporting the constraints linked to a differential sensor.

The present invention notably contradicts an a priori according to which turning over a target for a differential sensor is not useful because the sensor detects only one type of front, using the sequencing of the groups of teeth (1, 2, 4) in a direction and reverse sequencing (1, 4, 2) to allow the ECU to determine the type of four or three cylinder engine.

Figures 5 and 6 correspond to a 2' camshaft sprocket where:

- the first group of teeth 10' includes a tooth 11' providing the first four-cylinder engine rising edge mark and the first three-cylinder engine falling edge mark which, by way of example, has been positioned at +20°CRK,

- the second group of teeth 20' comprises four teeth 21', 22', 23' and 24', tooth 21' providing the first rising edge mark at 180°CRK, tooth 22' providing the second falling edge mark at 240 °CRK+20°CRK, tooth 23' constituting a synchronization tooth and tooth 24' providing the second rising edge marker at 360°CRK,

- the third group of teeth 30' comprises two teeth 31', 32', tooth 31' providing the third falling edge marker at 480°CRK+20°CRK while tooth 32 provides the fourth rising edge marker at 540°CRK .

It should be noted that the value of 20°CRK for the offsets of the falling edges of the three-cylinder engine is a value that simplifies the calculations, the minimum value to be chosen must be greater than Arctan(2.5/(R+h)) = 18 .5°CRK or 9.25°CAM. On the other hand, the invention does not impose a maximum distance for the offset of the falling edges with respect to the rising edges apart from the feasibility of the wheel in terms of the number of teeth.

It should be noted, however, that for reasons of cost and weight, we rather seek to have the smallest distance possible.

The sequence in the first direction of rotation according to arrow 3 is then represented in FIG. 5 with the rising edges 51', 52', 53', 54' of four-cylinder engine phasing, the falling edges 61', 62', 63' of the three-cylinder engine phasing and the synchronization slot 23' in the second group of teeth.

In the present invention, use is made of either the existence of sensors detecting pulses on rising edges or sensors detecting pulses on falling edges, or the direction of the target on its axis to differentiate three or four cylinder engines.

The invention, which makes it possible to produce a standardized target for compact 3 or 4 cylinder four-stroke engines such as two-wheel engines, is not limited to the examples shown and in particular, as indicated above, it is possible according to the proposed principle to position the synchronization tooth in the interval 20°CRK - 180°CRK even if this means adding two teeth in the interval 380°CRK - 480°CRK to keep three groups of teeth.

Claims (10)

Camshaft toothed wheel (2, 2a, 2b), forming a target for a camshaft position sensor (1), comprising a circular body provided with two opposite main faces and being provided on its circumference with a series of teeth, characterized in that said series of teeth comprises a minimum of six teeth and a maximum of seven teeth divided into three groups, for which in a given first direction of rotation (3) of the wheel, four teeth (4, 5, 7, 9) of said series whose rising edges spaced 90°CAM or 180°CRK constitute reference edges for determining the rotational position of a 4-cylinder engine, for which the falling edge of a first of these four teeth constitutes , with two descending edges of two additional teeth (6, 8) of said series, the reference edges spaced apart by 120°CAM or 240°CRK to determine the rotational position of a 3-cylinder engine and for which the angular distance between two teeth is greater than or equal to Arctan(4/(R+h))°CAM and the angular width of one tooth is greater than or equal to Arctan(2.5/(R+h))°CAM where R is the radius of the wheel excluding teeth and h is the height of the tooth expressed in mm. Camshaft toothed wheel according to Claim 1, in which the teeth of the series of teeth are grouped together in three groups of teeth (10, 20, 30, 10', 20', 30') successively provided with one (11 ), two (21, 22) and four (31, 32, 33, 34) teeth or one (11'), four (21', 22', 23', 24') and two (31', 32' ) teeth. Camshaft sprocket according to Claim 1 or 2, in which for a wheel with a radius of 15 mm excluding the teeth with the standard automotive tolerances, the minimum angular distance between two identical fronts is greater than or equal to Arctan(4/(R +h)) + Arctan(2.5/(R+h))°CAM. Camshaft sprocket according to Claim 1, 2 or 3, in which the teeth have the same angular width. Camshaft sprocket according to claim 4, wherein in said first direction of rotation (3):

1. the first group of teeth comprises an isolated tooth (11) whose rising edge corresponds to a 0° angle with a four-cylinder engine and the falling edge corresponds to a 0° angle with a three-cylinder engine;
2. the second group of teeth comprises two teeth (21, 22) such that the rising edge of the first of said two teeth corresponds to an angle of 180° CRK four-cylinder engine and the falling edge of the second of said two teeth corresponds to an angle of 240° CRK three-cylinder engine;
3. the third group of teeth comprises four teeth (31, 32, 33, 34) at equal angular distance from each other such that the rising edge of the first of said four teeth corresponds to an angle of 360° CRK four-cylinder engine, the second (32) of said four teeth is a synchronization tooth provided with a rising edge at 420°CRK and a falling edge at 440°CRK, the falling edge of the third (33) of said four teeth corresponds to an angle of 480°CRK three-cylinder engine and the rising edge of the last (34) of said four teeth corresponds to an angle of 540° CRK four-cylinder engine.

Camshaft sprocket according to claim 4, wherein in said first direction of rotation (3):

1. the first group of teeth (10') comprises an isolated tooth (11') whose rising edge corresponds to a 0° angle with a four-cylinder engine and the falling edge corresponds to a 0° angle with a three-cylinder engine;
2. the second group of teeth comprises four teeth (21', 22', 23', 24') at equal angular distance from each other such that the rising edge of the first (21') of said four teeth corresponds to an angle of 180 ° CRK four-cylinder engine, the falling edge of the second (22') of said four teeth corresponds to an angle of 240° CRK three-cylinder engine the third (23') of said four teeth is a synchronization tooth provided with a rising edge at 300°CRK and a falling edge at 320°CRK and the rising edge of the fourth (24') of said four teeth corresponds to an angle of 360° CRK four-cylinder engine;
3. the third group of teeth comprises two teeth such that the falling edge of the first (31') of said two teeth corresponds to an angle of 480° CRK three-cylinder engine and the rising edge of the second (32') of said two teeth corresponds to a 540° angle CRK four-cylinder engine.

Camshaft toothed wheel according to any one of the preceding claims, for which the angular width of the teeth is 10°CAM or 20°CRK and for which the reference falling edges at 120°CAM or 240°CRK of position three-cylinder engine in the first direction of rotation are offset by at least Arctan(2.5/(R+h))°CAM and preferably by +10°CAM or +20°CRK relative to the rising edges of the corresponding teeth. Engine control system comprising a computer (100) a crankshaft gear (70) and a crankshaft sensor (71), a camshaft gear (2) according to any one of the preceding claims and a crankshaft sensor gear (1) of the differential type, characterized in that the crankshaft toothed wheel and the camshaft toothed wheel are angularly keyed so that the crankshaft toothed wheel has a mark (gap) (81) keyed in a space devoid of the camshaft toothed wheel and for which the computer includes an engine synchronization algorithm (110) adapted to recognize the sequences formed by the groups of teeth of the camshaft toothed wheel and to deduce the engine position in real time. An engine control system according to claim 8, wherein, the differential camshaft sensor being selected to sense rising edges, the gear wheel is mounted in said first direction to sense 180° CRK edges for a four cylinder engine or is mounted in the opposite direction to the first direction to detect fronts at 240° CRK for a three-cylinder engine. An engine control system according to claim 8, wherein, the differential camshaft sensor being selected to sense falling edges, the gear wheel is mounted in said first direction to sense edges at 240° CRK for a three cylinder engine or is mounted in the opposite direction to the first direction to detect edges at 180° CRK for a four-cylinder engine.