Processing of signals from a crankshaft sensor

Abstract

Disclosed is a method for processing signals from a crankshaft sensor including the following steps: detection of a stopping of the engine; simulation and transmission of a backwards-running square waveform; and simulation and transmission of a forwards-running square waveform. Also disclosed is a processing module configured to implement such a method.

Claims

1. A method whereby a processing module (6) processes signals from a crankshaft sensor (1) in order to determine the position of an internal combustion engine upon a starting of said engine following a stopping thereof, said crankshaft sensor comprising a crankshaft wheel (2) comprising a determined number of teeth and at least one index (4) allowing a position in the revolution to be identified, said sensor being able, in combination with a processing device (5) for processing said signals, to determine the position of the crankshaft and direction of rotation of the crankshaft, from said signals comprising forwards-running and backwards-running square waveforms, the method comprising: detection of a stopping of said internal combustion engine, and, if the last square waveform received by the processing device (5) before the stopping of the engine corresponds to the engine rotating backwards: suspension of the transmission to the processing device (5) of an “engine stopped” status signal, and then simulation by the processing module (6) and transmission to the processing device (5) of a backwards-running square waveform (8), simulation by the processing module (6) and transmission to the processing device (5) of a forwards-running square waveform (9), leading to a detection by the processing device (5) that the crankshaft is running forwards, and, following the transmission of the two simulated square waveforms (8, 9) to the processing device (5), the lifting of said suspension and the transmission of the “engine stopped” status signal to the processing device (5).

2. The method as claimed in claim 1, wherein the transmission of the backwards-running square waveform (8) immediately follows the detection that the engine has stopped.

3. The method as claimed in claim 2, wherein the transmission of the forwards-running square waveform (9) is delayed after transmission of the backwards-running square waveform (8) by enough of a delay to render a noise filtering strategy inoperative.

4. The method as claimed in claim 2, wherein the speed is considered to be equal to a first constant mean value when only a single square waveform has been received, and/or the speed is calculated on the basis of the time between two square waveforms, or is considered to be equal to a second constant mean value when only two square waveforms have been received.

5. The method as claimed in claim 1, wherein the transmission of the forwards-running square waveform (9) is delayed after transmission of the backwards-running square waveform (8) by enough of a delay to render a noise filtering strategy inoperative.

6. The method of claim 5, wherein the delay is equal to 1 ms.

7. The method as claimed in claim 5, wherein the speed is considered to be equal to a first constant mean value when only a single square waveform has been received, and/or the speed is calculated on the basis of the time between two square waveforms, or is considered to be equal to a second constant mean value when only two square waveforms have been received.

8. The method as claimed in claim 1, wherein a calculation of the engine speed ignores the simulated backwards-running square waveform (8).

9. The method as claimed in claim 8, wherein the speed is considered to be equal to a first constant mean value when only a single square waveform has been received, and/or the speed is calculated on the basis of the time between two square waveforms, or is considered to be equal to a second constant mean value when only two square waveforms have been received.

10. The method as claimed in claim 1, wherein a calculation of the engine speed ignores the simulated backwards-running square waveform (8) and the simulated forwards-running square waveform (9).

11. The method as claimed in claim 10, wherein the speed is considered to be equal to a first constant mean value when only a single square waveform has been received, and/or the speed is calculated on the basis of the time between two square waveforms, or is considered to be equal to a second constant mean value when only two square waveforms have been received.

12. The method as claimed in claim 1, wherein the speed is considered to be equal to a first constant mean value, when only a single square waveform has been received, and/or the speed is calculated on the basis of the time between two square waveforms, or is considered to be equal to a second constant mean value when only two square waveforms have been received.

13. The method of claim 12, wherein the first constant mean value is 60 rpm.

14. The method of claim 13, wherein the second constant mean value is 90 rpm.

15. A processing module (6) for processing signals from a crankshaft sensor (1), the processing module being configured to implement the method as claimed in claim 2.

16. A processing module (6) for processing signals from a crankshaft sensor (1), the processing module being configured to implement the method as claimed in claim 5.

17. A processing module (6) for processing signals from a crankshaft sensor (1), the processing module being configured to implement the method as claimed in claim 8.

18. A processing module (6) for processing signals from a crankshaft sensor (1), the processing module being configured to implement the method as claimed in claim 10.

19. A processing module (6) for processing signals from a crankshaft sensor (1), the processing module being configured to implement the method as claimed in claim 12.

20. A processing module (6) for processing signals from a crankshaft sensor (1), the processing module being configured to implement the method as claimed claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and innovative advantages of the invention will become apparent from reading the following description, which is provided by way of non-limiting example, with reference to the accompanying drawings, in which:

(2) FIG. 1, which has already been described, illustrates the principle of a crankshaft sensor,

(3) FIG. 2, which has already been described, illustrates the mechanism for extrapolation and readjustment on receipt of a square waveform,

(4) FIG. 3, which has already been described, illustrates how the processing device behaves in the event that a backwards-running square waveform is received before a stopping of the engine, on an absolute diagram,

(5) FIG. 4, which has already been described, illustrates the same scenario as FIG. 3, on an offset diagram,

(6) FIG. 5 shows, on a diagram featuring the angular position in offset as a function of time, against a signal CRK, and illustrates the result of the invention, which makes it possible to ensure that the last square waveform received at the time of a stopping of the engine is always a forwards-running square waveform, and the associated advantages at the time of the restart.

(7) FIG. 6 illustrates the sequence of the steps of the method,

(8) FIG. 7 illustrates the situation of the invention

(9) FIG. 8 illustrates how the processing device behaves in the event that a forwards-running square waveform is received before a stopping of the engine, on an absolute diagram,

(10) FIG. 9 illustrates how the processing device behaves in the event that a forwards-running square waveform is received before a stopping of the engine, and shows the effect of the invention and the associated advantages at the time of the restart.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(11) For greater clarity, identical or similar elements have been designated by identical reference signs throughout the figures.

(12) In order to address the aforementioned problem, the invention comprises a processing module 6 capable of processing the signals and information from a crankshaft sensor 1.

(13) As illustrated in FIG. 7, a crankshaft sensor 1 transmits a signal containing square waveforms to a processing device 5 which processes it in order to maintain an absolute angular position of the crankshaft and therefore of the engine. The processing module 6 according to the invention is interposed between the crankshaft sensor 1 and the processing device 5.

(14) The aforementioned problem is greatly exacerbated by the fact that the last square waveform seen before the stopping of the engine is a backwards-running square waveform. It then follows, as described previously, that an unfavorable combination of poor knowledge of the speed and of erroneous assumptions as to the direction of rotation lead to a lack of precision in the estimating of the angular position at the time of the restart, which lack of precision lasts for at least three teeth/square waveforms.

(15) An important observation of the invention is that the problem does not occur at all, or at the very least has a markedly lesser impact on the estimate of the angular position, when the last square waveform received before the stopping of the engine is a forwards-running square waveform. This is illustrated in FIG. 8.

(16) As illustrated in FIG. 8, the engine stops between position #1 and position #2. As a result of the extrapolation, the estimated angular position continues until it becomes equal to #1, where it remains blocked. At the restart, the next square waveform #2 is correctly considered to be the square waveform #2 because the processing device still thinks that the engine is running forwards. A shallow gradient extrapolation is applied, as a precautionary measure, following the stopping of the engine. As a result, the estimate is pessimistic. On receipt of the next square waveform, this is correctly interpreted as being #3. The estimated angular position is immediately corrected by a rapid readjustment. Following square waveform #3, the extrapolation is too optimistic, because of the overcompensation associated with the steep gradient observed in the previous square waveform. At the next square waveform #4, the speed is now known with satisfactory precision and the extrapolation may be correct, as the two coincident curves testify.

(17) So, according to a novel idea of the invention, an operation is performed that is neutral so far as the angular position is concerned, but which places the system, and particularly the processing device 5, back in the favorable scenario in which the last square waveform received is a forwards-running square waveform.

(18) To do that, the invention simulates and transmits to the processing device 5 a succession of a backwards-running square waveform, 8, and of a forwards-running square waveform, 9. This can be seen in FIG. 9.

(19) The invention relates to a method for processing signals from a crankshaft sensor, comprising the following steps: The method is initiated by a detection that the engine has stopped. Such a detection is generally obtained when no square waveform has come from the crankshaft sensor 1 for a certain period of time, preferably 250 ms. According to one feature, this detection may be confirmed, for example by a subsequent recheck, after a longer interval of time, in order to avoid any false detection.

(20) According to an important feature of the invention, there is then a first step of simulating and transmitting a backwards-running square waveform, 8, followed by a second step of simulating and transmitting a forwards-running square waveform, 9. In this way, the processing module 6 simulates two successive square waveforms 8, 9, such as the crankshaft sensor 1 could have sent. These simulated square waveforms 8, 9 are transmitted to the processing device 5 as if they had come from the crankshaft sensor 1. Thus, according to the invention, the processing module 6 fools the processing device 5 by transmitting two extra square waveforms to it, in place of the crankshaft sensor 1.

(21) What then follows is that which can be described with reference to FIG. 5. The first row features the signal CRK from the crankshaft sensor 1. Underneath, and temporally aligned therewith, is a diagram indicating the angular position of the crankshaft, with the true position as a dotted line and the position as estimated by the processing device 5 as a solid line. The first square waveform on the left is the last square waveform received by the processing device 5 before the stopping of the engine. This is a backwards-running square waveform. The stopping of the engine occurs thereafter, and is featured by a double oblique stroke. After correction by the processing device 5, the estimated angular position of the engine is established as 0°. As soon as the absence of a square waveform (a steady state at 0°) is observed, it is determined that the engine has stopped and the method can begin. The processing module 6 simulates a backwards-running first square waveform 8 and a forwards-running second square waveform 9. These simulated square waveforms 8, 9 are transmitted to the processing device 5 as if they had come from the crankshaft sensor 1.

(22) On receipt of the backwards-running first square waveform 8, the processing device 5 decrements the angular position by one angular increment corresponding to one tooth. On receipt of the forwards-running second square waveform 9, the processing device 5 increments the angular position by one angular increment corresponding to one tooth. The angular position is once again 0′. The receipt of the two square waveforms 8, 9 is thus an operation that is neutral insofar as it does not alter the resultant angular position. However, at the next engine restart, the last square waveform seen by the processing device 5 is now a forwards-running square waveform.

(23) This feature completely changes the determination of the angular position at the following engine restart, as can be appreciated by comparison with the description given in relation to FIG. 4 in particular.

(24) After receiving the forwards-running second square waveform 9, the processing device 5 interpolates the angular position optimistically. The angular position rapidly becomes offset by one tooth. It remains confined to not exceeding this value until the square waveform #1, which is the first real square waveform, is received. On receipt of the square waveform #1, the offset is reset to zero. At that moment, two square waveforms, the second simulated square waveform 9 and the square waveform #1, can be used to determine an estimate of the speed by relating the angular length of a tooth to the time separating said two square waveforms 9 and #1. Failing that, by not retaining the second simulated square waveform 9, it is possible to consider a default mean speed, for example of 60 rpm. Because these two square waveforms are in the same direction, forwards, the extrapolation between the square waveforms #1 and #2 is, however, far more precise than the critical scenario. It can be seen from the figure that the error readjusted for on arriving at square waveform #2 is just 1.1°. Such an error is small enough to allow the engine control operations such as injection and/or ignition to be performed.

(25) Then, between the square waveforms #2 and #3 and then between the square waveforms #3 and #4, as the number of square waveforms increases, the precision of the calculation of the angular speed increases and the extrapolation of the angular position becomes all the more precise.

(26) The invention thus makes it possible to obtain enough precision on the angular position that injection and/or ignition can take place, and is advantageously able to do so as soon as the first real square waveform #1 is received, whereas the prior art entailed waiting for the 4th square waveform #4.

(27) It may advantageously be noted that the addition of two simulated square waveforms 8, 9 has no side effect on diagnostics or on safety. Due to the fact that these two square waveforms are of opposing direction, they cancel one another as far as the checks on the plausibility of the signal CRK from the crankshaft sensor 1 are concerned. In addition, the engine has physically stopped at the time at which these two simulated square waveforms 8, 9 are introduced. Thus, there is no risk of confusion with receipt of a square waveform resulting from the detection of an actual tooth. No diagnostics react to just two wave edges while an engine is stopped. No poor angular speed (engine speed) is exported.

(28) As illustrated in FIG. 9, from left to right, at the square waveform #1, the speed is known. Extrapolation is good with an estimate that coincides with the true angular position. The engine stops shortly after the square waveform #1. Extrapolation continues until position #2 is reached, which cannot be exceeded until a new square waveform is received. The falling wave edge of the first simulated square waveform 8 is then received. The processing device 5, still persuaded that the engine is running forwards, begins by incrementing the angular position. On receiving the rising wave edge of the first simulated square waveform 8, the processing device 5 realises that this is a backwards-running (BW) square waveform, and immediately corrects the angular position to position #1. The extrapolation continues, now in the backwards direction of running, with a gradient that is shallow on account of the change in direction. The falling wave edge of the second simulated square waveform 9 is then received. The processing device 5, persuaded that the engine is running backwards, begins by decrementing the angular position. On receiving the rising wave edge of the second simulated square waveform 9, it realises that this is a forwards-running (FW) square waveform, and immediately corrects the angular position to position #1. The extrapolation continues to increment, now in the forwards direction of running, with a gradient that is shallow on account of the stopping of the engine. However, this is too optimistic and the estimate reaches the position #2 before the corresponding square waveform #2 has been received. The estimate therefore awaits receipt of the square waveform #2. From #2 to #3, the extrapolation uses a first constant mean speed, for example 60 rpm, which turns out to be slightly optimistic. From #3 to #4, the extrapolation uses a second constant mean speed, for example 90 rpm, which turns out to be very slightly optimistic. After #4, the speed, after three square waveforms #1, #2, #3, is now known with precision and the extrapolation can use this speed: the two curves are coincident.

(29) According to one feature, the addition of the two simulated square waveforms according to the invention can be applied systematically as soon as a stopping of the engine is detected. Advantageously, said addition can be applied only when necessary, namely only when the last square waveform received before the stopping of the engine corresponds to a backwards rotation of the engine.

(30) According to the prior art, when a stopping of the engine is detected, an “engine stopped” status signal is transmitted to certain modules which require and use this information.

(31) This “engine stopped” status information is used for example by a starter controller which needs to ensure that the engine is stopped before allowing a restart. This is because activating the engine starter while the engine is running may damage the starter.

(32) According to the prior art, this transmission is performed as soon as the “engine stopped” status signal is produced. According to another advantageous feature of the invention, the transmission of the “engine stopped” status signal is, rather, suspended for at least the time taken for the two simulated square waveforms 8, 9 to be transmitted. Thus, even if the “engine stopped” status signal has been produced and available right from the start of the method, the transmission thereof is suspended. This suspension of the transmission is advantageously lifted after the two simulated square waveforms 8, 9 have been transmitted, so that said “engine stopped” status signal is transmitted to the module(s) concerned with processing it.

(33) In order not to waste time, the transmission of the simulated square waveforms 8, 9 needs to be performed rapidly so as not to interfere with a possible restart.

(34) According to another feature, the transmission of the backwards-running square waveform 8 is performed as quickly as possible, immediately following the detection that the engine has stopped.

(35) The same may be true of the transmission of the forwards-running square waveform 9. However, a noise filtering strategy may be implemented on the input side of the processing device 5. Such a strategy could eliminate a second square waveform 9 appearing too soon after the first square waveform 8. Thus, according to another feature, the transmission of the second square waveform 9 is advantageously delayed after transmission of the backwards-running square waveform 8. The delay applied in this case is just enough to render the noise filtering strategy inoperative. This delay is preferably equal to 1 ms.

(36) As illustrated in FIG. 6, the method begins by waiting 10 for the engine to stop. When such an engine stop (Stop) is detected, a backwards-running square waveform 8 is simulated (BW) and transmitted 11. A delay 12 is then applied (ΔT) if appropriate, in order to avoid unwanted filtering. A forwards-running square waveform 9 is then simulated (FW) and transmitted 13. Thereafter, the “engine stopped” status signal (Stop), which had been delayed, can then be transmitted 14.

(37) In order not to interfere with the calculation of the speed, the simulated square waveforms 8, 9, which do not correlate with an actual movement of the crankshaft wheel 2, can be disregarded in the speed calculation. According to one feature, the first simulated square waveform 8 is ignored in calculating the speed. According to one feature, the first simulated square waveform 8 and the second simulated square waveform 9 are ignored in calculating the speed.

(38) The two simulated square waveforms 8, 9 do not in any way interfere with the engine control functions because the engine has not yet been declared to have stopped. The engine may still possibly hiccup.

(39) Conventionally according to the prior art, the speed is calculated with precision using a three-term recurrence formula, using the last three square waveforms. So, in a restart, it is necessary to find another approach while three square waveforms, be they real square waveforms or simulated square waveforms, have not yet been received.

(40) According to another feature of the invention, the speed is considered to be equal to a first constant mean value when only one square waveform has been received. This constant mean value is preferably equal to 60 rpm, which constitutes an approximation of the speed of an engine on starting.

(41) According to another feature of the invention, the speed is considered to be equal to a second constant mean value when only two square waveforms have been received. This constant mean value is preferably equal to 90 rpm.

(42) The two values of 60 and 90 rpm are indicative. They correspond to values observed on a given engine with a standard nominal battery voltage.

(43) According to another feature, the speed is calculated on the time between two square waveforms when only two square waveforms have been received.

(44) Thereafter, as soon as at least three square waveforms have been received, the formula of the prior art may advantageously be employed.

(45) The invention also relates to a processing module 6 configured to implement the method described hereinabove.

(46) The invention has been described above by way of example. It will be understood that a person skilled in the art is able to produce different variant embodiments of the invention, for example by combining the various features above taken alone or in combination, without departing from the scope of the invention in doing so.