Method for communicating a malfunction of a system for measuring speed and direction of rotation of a rotary shaft

Abstract

The subject of the present invention is a method for communicating a malfunction of a system for measuring speed and direction of rotation of a rotary shaft, said system comprising: a toothed wheel associated with said rotary shaft, called target (14), a magnetic field sensor (10′), measuring values (K, A) of the magnetic field (B, B′, B″) generated by the passage of the teeth (T1, T2 . . . Ti) in front of said sensor (10′) and delivering a signal (S, S′, S″) to processing means 13). According to the invention, the method comprises the following steps: step 1: comparison by the sensor between the measured values and predetermined threshold values of the magnetic field, step 2: if the measured values are below the predetermined threshold values, step 3: generation by the sensor of a coding on the signal, representative of the measured values, to communicate a malfunction of the system to the processing means.

Claims

1. A method for communicating a malfunction of a system for measuring speed and direction of rotation of a rotary shaft to processing means (13), said system comprising: a toothed wheel associated with said rotary shaft, called target (14), a magnetic field sensor (10, 10′), measuring values (K, A) of the magnetic field (B, B′, B″) generated by the passage of the teeth (T1, T2 . . . Ti) in front of said sensor (10′) and delivering a signal (S, S′, S″) to the processing means (13), said signal (S, S′, S″) comprising pulses (I) between a high state and a low state, each pulse (I) being representative of the passage of a tooth (T1, T2 . . . Ti) in front of the sensor (10′), and each pulse (I) having two predetermined durations, a first duration (t1) representative of a first direction of rotation of the target (14), and a second duration (t2) representative of the opposite direction of rotation of the target (14), wherein the detection method comprises the following steps: step 1: comparison by the sensor (10′) between the measured values (A, K) of the magnetic field (B, B′, B″) and predetermined threshold values (A.sub.ref, K.sub.ref) of the magnetic field (B, B′, B″), step 2: if the measured values (A, K) of the magnetic field (B, B′, B″) are below the predetermined threshold values (A.sub.ref, K.sub.ref) of the magnetic field (B, B′, B″), then step 3: generation by the sensor (10′), in a direction of rotation of the target (14), of a coding of the signal (S′, S″), representative of the measured values (A, K) of the magnetic field (B, B′, B″), by using at least one third pulse duration (t3) and at least one fourth pulse duration (t4) in order to communicate a malfunction of the system for measuring speed and direction of rotation of the rotary shaft to the processing means (13).

2. The detection method, as claimed in claim 1, wherein the coding is binary (0, 1), the third predetermined duration (t3) having the value “0”, and the fourth predetermined duration (t4) having the value “1”.

3. The detection method, as claimed in claim 2, wherein one of the measured values (A) of the magnetic field (B, B′, B″) is the amplitude of the magnetic field (B, B′, B″) during at least one revolution of the target (14).

4. The detection method, as claimed in claim 2, wherein one of the measured values (K) of the magnetic field (B, B′, B″) is the ratio between the minimum amplitude (A.sub.MIN) of the magnetic field and the maximum amplitude (A.sub.MAX) of the magnetic field during at least one revolution of the target (14).

5. The detection method, as claimed in claim 2, wherein the third predetermined duration (t3) and the fourth predetermined duration (t4) are computed as a function of the time between the passage of two consecutive teeth (T1, T2 . . . Ti) at a maximum speed of rotation of the target (14).

6. The detection method, as claimed in claim 1, wherein one of the measured values (A) of the magnetic field (B, B′, B″) is the amplitude of the magnetic field (B, B′, B″) during at least one revolution of the target (14).

7. The detection method, as claimed in claim 6, wherein the third predetermined duration (t3) and the fourth predetermined duration (t4) are computed as a function of the time between the passage of two consecutive teeth (T1, T2 . . . Ti) at a maximum speed of rotation of the target (14).

8. The detection method, as claimed in claim 1, wherein one of the measured values (K) of the magnetic field (B, B′, B″) is the ratio between the minimum amplitude (A.sub.MIN) of the magnetic field and the maximum amplitude (A.sub.MAX) of the magnetic field during at least one revolution of the target (14).

9. The detection method, as claimed in claim 8, wherein the third predetermined duration (t3) and the fourth predetermined duration (t4) are computed as a function of the time between the passage of two consecutive teeth (T1, T2 . . . Ti) at a maximum speed of rotation of the target (14).

10. The detection method, as claimed in claim 1, wherein the third predetermined duration (t3) and the fourth predetermined duration (t4) are computed as a function of the time between the passage of two consecutive teeth (T1, T2 . . . Ti) at a maximum speed of rotation of the target (14).

11. A magnetic field sensor (10′) of a system for measuring speed and direction of rotation of a rotary shaft, measuring values (A, K) of the magnetic field generated by the passage of the teeth (T1, T2 . . . Ti) of a toothed wheel associated with said rotary shaft, called target (14), in front of said sensor (10) and delivering a signal (S, S′, S″) to processing means (13), said signal (S, S′, S″) comprising pulses (I) between a high state and a low state, each pulse (I) being representative of the passage of a tooth (T1, T2 . . . Ti) in front of the sensor (10′), and each pulse (I) having two predetermined durations, a first duration (t1) representative of a first direction of rotation of the target (14), and a second duration (t2) representative of the opposite direction of rotation of the target (14), wherein said sensor (10) comprises: storage means (30) for predetermined threshold values (A.sub.ref, K.sub.ref) of the magnetic field (B, B′, B″), comparison means (31) between the measured values (A, K) of the magnetic field (B, B′, B″) and the predetermined threshold values (A.sub.ref, K.sub.ref) of the magnetic field (B, B′, B″), means (32) for generating at least one third predetermined pulse duration (t3) and at least one fourth predetermined pulse duration (t4), to produce a binary coding of the signal (S′, S″), representative of the measured values (A, K) of the magnetic field (B, B′, B″), intended for the processing means (13).

12. A motor vehicle comprising a magnetic field sensor (10′) as claimed in claim 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages of the invention will become apparent on reading the following description and on studying the attached drawings in which:

(2) FIG. 1, explained previously, is a schematic cross-sectional view, representing a sensor 10 of a crankshaft 16 and its associated target 14,

(3) FIG. 2, explained previously, represents the position of the teeth T.sub.1, T.sub.2 . . . T.sub.i and of the hollows C.sub.1, C.sub.2 . . . C.sub.i of the target 14,

(4) FIG. 3, explained previously, represents, according to the prior art, the signal B delivered by the sensor 10 as a function of the angle of rotation θ of the crankshaft 16 (or of the target 14), and the detection threshold S.sub.1 for the rising and falling edges, relative to the passage of teeth T.sub.1, T.sub.2 . . . T.sub.i and of the hollows C.sub.1, C.sub.2 . . . C.sub.i of the target 14 of FIG. 2 in front of the sensor 10,

(5) FIG. 4, explained previously, represents the signal S delivered by the sensor 10 to the processing means 13,

(6) FIG. 5 represents the variations of the magnetic field B′ perceived by the sensor 10 according to the angle of rotation θ of the crankshaft 16, upon a malfunction of the system, due to an air gap defect between the sensor 10 and the target 14,

(7) FIG. 6 represents, according to the invention, the binary coding of the malfunction illustrated in FIG. 5, produced by the sensor 10 on the signal S′ intended for the processing means,

(8) FIG. 7 represents the variations of the magnetic field B″ perceived by the sensor 10 according to the angle of rotation of the target, upon a malfunction of the system, due to a “radial runout” of the target (or of the crankshaft),

(9) FIG. 8 represents, according to the invention, the binary coding of the malfunction illustrated in FIG. 7, produced by the sensor 10 on the signal S′ intended for the processing means,

(10) FIG. 9 represents the magnetic field sensor 10′ according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(11) FIG. 1 illustrates a system 20 for measuring speed and direction of rotation of a crankshaft comprising: a toothed wheel associated with the crankshaft (not represented), called target 14, a magnetic field sensor 10 or crankshaft sensor measuring values of the magnetic field, for example the intensity of the magnetic field, generated by the passage of the teeth C.sub.1, C.sub.2 . . . C.sub.i of the target 14 in front of said sensor 10.

(12) The sensor 10 delivers a 0-5 V signal S to processing means 13, said signal comprises pulses I between a high state (5 V) and a low state, for example from a high state to a low state (0 V) (see FIG. 4). Each pulse I is representative of the passage of a tooth T.sub.1, T.sub.2 . . . T.sub.i (more specifically of the passage of half of a tooth) in front of the sensor 10, and each pulse I has two predetermined durations, a first predetermined duration t1, representative of a first direction of rotation of the target 14, for example forward A.sub.V and a second predetermined duration t2, representative of the opposite direction of rotation of the target 14, that is to say reverse A.sub.R.

(13) The signal S is received by the processing means 13 which deduces therefrom the speed and the direction of rotation of the crankshaft.

(14) This is known to those skilled in the art and has been described previously.

(15) The invention will be described below by taking as example of malfunction of the system 20, first, a malfunction of air gap defect type, then, secondly, a malfunction of “radial runout” of the target 14 (i.e. of the crankshaft) type.

(16) In the case of an air gap defect, the sensor 10 is abnormally far away from the target 14. This can occur when mounting the sensor 10. Because of the distance of the sensor 10 from the target 14 the sensor perceives, from the target 14, a weakened magnetic field B′, of low intensity. This is represented in FIG. 5. The amplitude value A measured by the sensor 10, that is to say the difference between the maximum value of the magnetic field B.sub.MAX2 and the minimum value of the magnetic field B.sub.MIN2, i.e. A=(B.sub.MAX2−B.sub.MIN2), is greatly reduced relative to the amplitude value of the magnetic field B of the prior art A.sub.ref=(B.sub.MAX1−B.sub.MIN1), i.e.:
(B.sub.MAX2−B.sub.MIN2)<(B.sub.MAX1−B.sub.MIN1)

(17) The value of the detection threshold S2 in the presence of this air gap defect is much smaller than that of the detection threshold (S1) for a normal air gap, which renders the detection of the teeth T.sub.1, T.sub.2 . . . Ti of the target 14 more inaccurate.

(18) The invention proposes that the sensor 10′ compares the measured value A of the magnetic field B′, in this example, the amplitude of the magnetic field A=B.sub.MAX2−B.sub.MIN2, and compares it to a predetermined amplitude threshold value representative of the absence of air gap defect, this amplitude threshold value corresponding to the minimum amplitude of the magnetic field, for example here A.sub.ref=B.sub.MAX1−B.sub.MIN1, obtained with a maximum air gap distance.

(19) To this end, the sensor 10′ according to the invention comprises, in software form, storage means 30 (see FIG. 9) for predetermined threshold values of the magnetic field B (here, the amplitude threshold value A.sub.ref) and comparison means 31 (see FIG. 9), between the measured values (here the amplitude A) of the magnetic field B′ and the predetermined threshold values A.sub.ref of the magnetic field B.

(20) If the measured value, here the amplitude A of the magnetic field B′, is below the predetermined amplitude threshold value A.sub.ref, the sensor 10′ informs the processing means 13 thereof by producing, on the output line of the signal S′, a coding representative of the measured value, that is to say of the measured amplitude A of the magnetic field B′.

(21) To this end, the sensor 10′ generates, on the signal S, pulses I of predetermined durations, by using a third predetermined duration t3, for example equal to 135 μs and a fourth predetermined duration t4, for example equal to 170 μs, different from the first predetermined duration t1=45 μs indicating the “forward” direction of rotation A.sub.V of the target 14, and different from the second predetermined duration t2=90 μs, indicating the “reverse” direction of rotation A.sub.R of the target 14. The generation of these third t3 and fourth t4 predetermined durations is performed by generation means 32 (see FIG. 9) of software type incorporated in the sensor 10.

(22) In the nonlimiting example below, the coding produced is a binary coding, using a succession of pulses I of third t3 and of fourth t4 predetermined durations.

(23) This is illustrated in FIG. 6. Once the sensor 10′ has detected that the amplitude A of the measured magnetic field B′ was below the predetermined amplitude threshold value A.sub.ref of the magnetic field B for a normal air gap, it generates, on its signal S output line, a binary code representative of the measured amplitude A of the magnetic field, by assigning the value “0” for example to the third predetermined duration t3, and a value “1” to the fourth predetermined duration t4.

(24) In FIG. 6, the binary code produced is on 8 bits, and consists of “0 1 0 1 1 1 0 0”. This code is received by the processing means 13, which extracts therefrom the value of the measured amplitude A and sends to a central unit a message indicating air gap defect between the sensor 10 and the target 14.

(25) FIG. 7 illustrates the variations of the magnetic field B″ perceived by the sensor 10 in the case of a malfunction of the system, of “radial runout” type.

(26) In this case, the amplitude of the magnetic field B″ is not constant, it varies between a maximum amplitude A.sub.MAX=B.sub.MAX4−B.sub.MIN4 and a minimum amplitude A.sub.MIN=B.sub.MAX3−B.sub.MIN3.

(27) In this case, the sensor 10′ compares the ratio between the minimum amplitude and the maximum amplitude of the measured magnetic field B″, i.e.

(28) $K=\frac{A_{\mathrm{MIN}}}{A_{\mathrm{MAX}}}=\frac{\left(B_{\mathrm{MAX}3}-B_{\mathrm{MIN}3}\right)}{\left(B_{\mathrm{MAX}4}-B_{\mathrm{MIN}4}\right)}$
with a predetermined ratio threshold value K.sub.ref.

(29) The predetermined ratio threshold value K.sub.ref represents the minimum ratio between the minimum amplitude and the maximum amplitude of the magnetic field B, obtained without “radial runout” type system malfunction.

(30) In the example illustrated in FIG. 8, K<K.sub.ref, for example K.sub.ref is equal to 0.7.

(31) The binary coding produced on the signal S″ representative of the value of the amplitude ratio K and illustrated in FIG. 8, is for example equal to “1 1 1 1 0 0 0 0”.

(32) This binary code is received by the processing means 13 which extracts therefrom the value of the amplitude ratio K and sends a “radial runout” defect message to a central unit.

(33) Obviously, the sensor 10′ can use a plurality of predetermined durations, depending on the complexity of the code and therefore of the message to be transmitted to the processing means 13.

(34) It is important to note that the binary coding can be produced only in one direction of rotation of the target 14, for example forward A.sub.V. In effect, by generating the defect binary code, that is to say by replacing the predetermined pulse duration representative of the direction of rotation of the target 14 (either the first predetermined duration t1 or the second predetermined duration t2) by the third and fourth predetermined durations t3, t4, representative of the defect, the processing means 13 no longer receive the information concerning the direction of rotation of the target 14. This is resolved by the invention, by producing the binary coding only in a given direction of rotation, for example forward A.sub.V.

(35) When the direction of rotation of the target 14 changes, and switches from forward A.sub.V to reverse A.sub.R, the coding is interrupted. The detection of the direction of rotation of the target 14 is known to those skilled in the art and has been described previously.

(36) Furthermore, the value of the third predetermined duration t3 and of the fourth predetermined duration t4 must be calculated so as to be less than the duration between two successive teeth as the maximum speed of rotation (for example 4000 rpm or 6000 rpm) of the target 14, in order to be able to signal any defect of the system at this maximum speed.

(37) According to the invention, the method for communicating a malfunction of a system for measuring the speed and the direction of rotation of a rotary shaft, in our example, a crankshaft, with processing means, therefore comprises the following steps: step 1: comparison by the sensor 10′ between the measured values of the magnetic field and predetermined threshold values of the magnetic field, step 2: if the measured values of the magnetic field are below the predetermined threshold values of the magnetic field, then step 3: generation by the sensor 10′, in a direction of rotation of the target 14, of a coding of the signal S′, S″, representative of the measured values of the magnetic field, by using at least one third pulse duration t3 and at least one fourth pulse duration t4 in order to communicate a malfunction of the system for measuring speed and direction of rotation of the rotary shaft to the processing means 13.

(38) To implement the communication method according to the invention, the sensor 10′ comprises: storage means 30 for predetermined threshold values A.sub.ref, K.sub.ref of the magnetic field, comparison means 31 between the measured values A, K of the magnetic field and the predetermined threshold values A.sub.ref, K.sub.ref of the magnetic field, means 32 for generating at least one third predetermined pulse duration t3 and at least one fourth predetermined pulse duration t4, to produce a binary coding of the signal S′, S″, representative of the measured values A, K of the magnetic field intended for the processing means 13.

(39) Obviously, the measured values of the magnetic field may be different from the amplitude or from the amplitude ratio (ratio between the minimum amplitude and the maximum amplitude) of the magnetic field. Depending on the measured values and the predetermined threshold values of the magnetic field, the step 3 can be carried out when the measured values are above the predetermined threshold values. Such is the case, for example, if the chosen measured value is the ratio of amplitude between the maximum amplitude and the minimum amplitude.

(40) Obviously, it is possible to envisage setting the predetermined threshold values A.sub.ref, K.sub.ref of the magnetic field B such that all the measured values A, K of the magnetic field B are below the predetermined threshold values A.sub.ref, K.sub.ref. In this case, for example, after each first revolution of the target 14, the sensor 10′ informs the processing means 13 of the measured values A, K by producing the coding of the measured values A, K on the signal S.

(41) The invention can therefore be implemented by simple modification of the software included in the sensor 10′. Obviously, the processing means 13 are adapted to decode the signal S′, S″ from the sensor 10′.

(42) The invention therefore makes it possible to communicate a malfunction of the system for measuring the speed and the direction of rotation of the crankshaft to the processing means, in this case more particularly an assembly defect, incorrect air gap between the sensor and the target, “radial runout” defect, or defect of eccentricity of the target 14 and this at low cost, since, to carry out the malfunction communication method according to the invention, only modifications of software type need to be made to the sensor.