METHOD FOR SYNCHRONISING AN INTERNAL COMBUSTION ENGINE

Abstract

A method for synchronizing an internal combustion engine includes: a) a first step of acquiring, by the camshaft sensor, signals corresponding to at least five cam edges x; b) a second step of determining the value, from the camshaft signal, of a first, second and third actual ratio; c) a third step of establishing, for each actual value ratio obtained in b), a list of possible cam edges x by comparing the values of the first, second and third actual ratios, respectively, with a tolerance window corresponding to a value of a first, second or third theoretical ratio for a given cam edge x, each weighted by a tolerance factor k; and d) a fourth step of determining the cam edge x seen by the camshaft sensor, the cam edge actually seen by the sensor corresponding to the cam edge x common to the three lists established in c).

Claims

1. A method for synchronizing an internal combustion engine comprising at least one cylinder, at least one piston movable in the at least one cylinder and driving a crankshaft cooperating with a camshaft, said camshaft cooperating with a known target of the camshaft having a number of cam edges x, and a camshaft sensor generating a camshaft signal as a function of the number of cam edges x, said method comprising: a) a first step of acquiring, by the camshaft sensor, signals corresponding to at least five cam edges x, b) a second step of determining the value, from the camshaft signal, of a first, second and third actual ratio (N1, N2, N3) for a given cam edge x, c) a third step of establishing, for each actual ratio value (N1, N2, N3) obtained in the second step, a list of possible cam edges x by comparing the values of the first, second and third actual ratios (N1, N2, N3), respectively, with a tolerance window corresponding to a value of a first, second or third theoretical ratio (T1, T2, T3) for a given cam edge x, each weighted by a tolerance factor k, and d) a fourth step of determining the cam edge x seen by the camshaft sensor, the cam edge actually seen by the sensor corresponding to the cam edge x common to the three lists established in the third step.

2. The method as claimed in claim 1, wherein a cam edge x is considered possible when the values of the first, second and third actual ratios (N1, N2, N3) are, respectively, within an interval [T1/k; T1*k], [T2/k; T2*k] and [T3/k; T3*k] for a given cam edge x.

3. The method as claimed in claim 1, wherein the tolerance factor k is a constant number belonging to the set between 1.5 and 3.

4. The method as claimed in claim 1, wherein the first, second and third theoretical ratios (T1, T2, T3) are determined from the angles a between the cam edges x and are of the following formulas:
T1=(T.sub.a+T.sub.a-2)/(T.sub.a-1+T.sub.a-3)
T2=(T.sub.a+T.sub.a-1)/(T.sub.a-2+T.sub.a-3), and
T3=(T.sub.a+T.sub.a-3)/(T.sub.a-1+T.sub.a-2), where T.sub.a is the angle between the cam edges x and x-1, T.sub.a-1 is the angle between the cam edges x-1 and x-2, T.sub.a-2 is the angle between the cam edges x-2 and x-3, and T.sub.a-3 is the angle between the cam edges x-3 and x-4.

5. The method as claimed in claim 1, wherein the first, second and third actual ratios (N1, N2, N3) are determined from the measurement of the times separating the cam edges x and satisfy the following formulas:
N1=(T.sub.1+T.sub.n-2)/(T.sub.n-1+T.sub.n-3),
N2=(T.sub.1+T.sub.n-1)/(T.sub.n-2+T.sub.n-3), and
N3=(T.sub.1+T.sub.n-3)/(T.sub.n-1+T.sub.n-2), where T.sub.1 is the time between the last two cam edges seen by the sensor, T.sub.n-1 is the time between the penultimate and the third-last cam edge seen by the sensor, T.sub.n-2 is the time between the third-last and the fourth-last cam edge seen by the sensor, and T.sub.n-3 is the time between the fourth-last and the fifth-last cam edges seen by the sensor.

6. The method as claimed in claim 2, wherein the tolerance factor k is a constant number belonging to the set between 1.5 and 3.

7. The method as claimed in claim 1, wherein the tolerance factor k is a constant number belonging to the set to 2.3.

8. The method as claimed in claim 2, wherein the tolerance factor k is a constant number belonging to the set to 2.3.

9. The method as claimed in claim 2, wherein the first, second and third actual ratios (N1, N2, N3) are determined from the measurement of the times separating the cam edges x and satisfy the following formulas:
N1=(T.sub.1+T.sub.n-2)/(T.sub.n-1+T.sub.n-3),
N2=(T.sub.1+T.sub.n-1)/(T.sub.n-2+T.sub.n-3), and
N3=(T.sub.1+T.sub.n-3)/(T.sub.n-1+T.sub.n-2), where T.sub.n is the time between the last two cam edges seen by the sensor, T.sub.n-1 is the time between the penultimate and the third-last cam edge seen by the sensor, T.sub.n-2 is the time between the third-last and the fourth-last cam edge seen by the sensor, and T.sub.n-3 is the time between the fourth-last and the fifth-last cam edges seen by the sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Further features, advantages and details of the invention will be better understood from the following further description in conjunction with the drawing, in which:

[0036] FIG. 1 shows an example of a camshaft signal generated by a camshaft sensor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] An internal combustion engine generally consists of at least one cylinder and at least one piston movable between a top position and a bottom position in the at least one cylinder. The position of the reference tooth is known and makes it possible to associate each tooth of the crankshaft signal with an engine position. In particular, the crankshaft cooperates with a camshaft, which in turn cooperates with a camshaft target having a number of cam edges x spaced apart from each other by an angle a. In an internal combustion engine, the configuration of the camshaft target is known. The engine also comprises a camshaft sensor that generates a camshaft signal as a function of the number of cam edges x. Thus, for a given camshaft target, the resulting camshaft signal is also known.

[0038] The internal combustion engine is then synchronized when the cam edge x actually seen by the camshaft sensor is known.

[0039] FIG. 1 is an example of a camshaft signal generated by a camshaft sensor. In this example, the camshaft signal has eight cam edges x.sub.1, x.sub.2 x.sub.3, x.sub.4, x.sub.5, x.sub.6 x.sub.7 and x.sub.8. For each of the camshaft edges x, it is possible to determine a first T1, a second T2 and a third T3 theoretical ratio. Said first, second and third theoretical ratios are determined from the angles a between the cam edges x and are of the following formulas:

T1=(T.sub.a+T.sub.a-2)/(T.sub.a-1+T.sub.a-3)

T2=(T.sub.a+T.sub.a-1)/(T.sub.a-2+T.sub.a-3), and

T3=(T.sub.a+T.sub.a-3)/(T.sub.a-1+T.sub.a-2), [0040] where [0041] T.sub.a is the angle between the cam edges x and x-1, [0042] T.sub.a-1 is the angle between the cam edges x-1 and x-2, [0043] T.sub.a-2 is the angle between the cam edges x-2 and x-3, and [0044] T.sub.a-3 is the angle between the cam edges x-3 and x-4.

[0045] Thus, for each cam edge x, three theoretical ratios are available and each theoretical ratio is weighted by a tolerance factor k so as to define a tolerance window. The limits of this tolerance window are obtained by dividing and multiplying the theoretical ratio by the tolerance factor k.

[0046] This tolerance factor k is dependent in particular on the parameters of the internal combustion engine, but also takes into account speed variations when starting the engine, moreover under conditions such as a cold start or with a weak battery. The tolerance factor k is a constant number in the range of 1.5 to 3, preferably 2.3.

[0047] For each cam edge x, there are three theoretical ratios T1, T2, T3 and, for each ratio T1, T2, T3, there is a tolerance window corresponding to [T1/k; T1*k], [T2/k; T2*k] and [T3/k; T3*k].

[0048] Thus, for the example related to FIG. 1, the angle a.sub.1 between the cam edges x8 and x.sub.1 is equal to 30 degrees. The angle a2 between the cam edges x.sub.1 and x2 is equal to 150 degrees. The angle a.sub.3 between the cam edges x2 and x.sub.3 is equal to 30 degrees. The angle a.sub.4 between the cam edges x.sub.3 and x.sub.4 is equal to 30 degrees. The angle as between the cam edges x.sub.4 and x.sub.5 is equal to 150 degrees. The angle a.sub.6 between the cam edges x.sub.5 and x.sub.6 is equal to 90 degrees. The angle a.sub.7 between the cam edges x.sub.6 and x.sub.7 is equal to 90 degrees. The angle a.sub.8 between the cam edges x.sub.7 and x.sub.8 is equal to 150 degrees. All the angular values are expressed in degrees crank angle and one camshaft revolution represents 7200 crank angle.

[0049] These data make it possible to obtain the theoretical ratios T1, T2 and T3 as well as the limits of the corresponding tolerance windows for each cam edge x. For the example related to FIG. 1, the data are illustrated in tables 1 to 3 below. Table 1 shows the data in relation to the first theoretical ratio T1, table 2 shows the data in relation to the second theoretical ratio T2, and table 3 shows the data in relation to the third theoretical ratio T3. The coefficient k was set to 2.3.

TABLE-US-00001 TABLE 1 Cam edges x.sub.1 x.sub.2 x.sub.3 x.sub.4 x.sub.5 x.sub.6 x.sub.7 x.sub.8 T1 0.5 2.5 0.2 3.0 1 0.67 2 1 T1/k 1.15 5.75 0.46 6.9 2.3 1.53 4.6 2.3 T1*k 0.217 1.087 0.087 1.304 0.44 0.29 0.87 0.44

TABLE-US-00002 TABLE 2 Cam edges x.sub.1 x.sub.2 x.sub.3 x.sub.4 x.sub.5 x.sub.6 x.sub.7 x.sub.8 T2 1 0.75 1 0.333 1 4 1 1 T2/k 2.3 1.725 2.3 0.767 2.3 9.2 2.3 2.3 T2*k 0.44 0.326 0.44 0.145 0.44 1.74 0.44 0.44

TABLE-US-00003 TABLE 3 Cam edges x.sub.1 x.sub.2 x.sub.3 x.sub.4 x.sub.5 x.sub.6 x.sub.7 x.sub.8 T3 0.5 1.333 1 0.333 5 0.67 0.5 1.667 T3/k 1.15 3.067 2.3 0.767 11.5 1.53 1.15 3.833 T3*k 0.217 0.58 0.44 0.145 2.174 0.29 0.22 0.725

[0050] The method according to the invention allows the engine to be quickly synchronized during start-up, for example, by using theoretical data.

[0051] The method according to the invention includes determining 3 actual ratios N1, N2 and N3, each determined from the measurement of the times separating the cam edges x and satisfying the following formulas:

N.sub.1=(T.sub.n+T.sub.n-2)/(T.sub.n-1+T.sub.n-3),

N2=(T.sub.n+T.sub.n-1)/(T.sub.n-2+T.sub.n-3), and

N3=(T.sub.n+T.sub.n-3)/(T.sub.n-1+T.sub.n-2), [0052] where [0053] T.sub.n is the time between the last two cam edges seen by the sensor, [0054] T.sub.n-1 is the time between the penultimate and the third-last cam edge seen by the sensor, [0055] T.sub.n-2 is the time between the third-last and the fourth-last cam edge seen by the sensor, and [0056] T.sub.n-3 is the time between the fourth-last and the fifth-last cam edges seen by the sensor.

[0057] Thus, it is necessary for the camshaft sensor to acquire five signals corresponding to at least five cam edges x. Once the fifth cam edge x is detected by the sensor, the method according to the invention makes it possible to determine which cam edge x it corresponds to and thus to synchronize the engine.

[0058] Once the five cam edges have been acquired, it is possible to determine the value of a first, second and third actual ratio (N1, N2, N3).

[0059] Each actual ratio calculated makes it possible to establish a list of possible cam edges x for this fifth cam edge detected by the camshaft sensor. These lists are obtained by comparing the value of the actual ratios N1, N2 and N3 with the tolerance windows corresponding to the value of the first, second or third theoretical ratio for a given cam edge x. Thus, a cam edge x is considered possible when the values of the first, second and third actual ratios (N1, N2, N3) are, respectively, within an interval [T1/k; T1*k], [T2/k; T2*k] and [T3/k; T3*k] for a given cam edge x.

[0060] It follows that the cam edge x actually seen by the sensor corresponds to the cam edge x common to the previously established lists.

[0061] In the example in relation to FIG. 1 and in relation to tables 1, 2 and 3, if the following data are taken for the calculation of the first, second and third actual ratios: [0062] Tn=30, [0063] Tn-1=150, [0064] Tn-2=90, and [0065] Tn-3=90.

[0066] This makes it possible to calculate the actual ratios: [0067] N1=0.5 [0068] N2=1 [0069] N3=0.5

[0070] The list established in relation to the first theoretical ratio T1 makes the cam edges x.sub.1, x.sub.5, x.sub.6 and x.sub.8 possible because N1 is within the tolerance interval of the cam edges x.sub.1, x.sub.5, x.sub.6 and x.sub.8 for the first theoretical ratio T1.

[0071] The list established in relation to the second theoretical ratio T2 makes the cam edges x.sub.1, x2, x.sub.3, x.sub.5, x.sub.7 and x.sub.8 possible because N2 is within the tolerance interval of the cam edges x.sub.1, x.sub.2, x.sub.3, x.sub.5, x.sub.7 and x.sub.8 for the second theoretical ratio T2.

[0072] The list established in relation to the third theoretical ratio T3 makes the cam edges x.sub.1, x.sub.3, x.sub.4, x.sub.6 and x.sub.7 possible because N3 is within the tolerance interval of the cam edges x.sub.1, x.sub.3, x4, x6 and x7 for the third theoretical ratio T3.

[0073] The method according to the invention retains only the possible edges common to all three lists. In the previous example, only edge x.sub.1 is common. The algorithm then determines that the last edge seen is edge number 1.

[0074] The method according to the invention thus makes it possible to synchronize an internal combustion engine without the need for data provided by a crankshaft sensor and also as soon as the camshaft sensor detects only 5 cam edges.