Method for monitoring and storing the angular position of a combustion engine by means of a camshaft sensor

Abstract

The invention proposes a method for monitoring the angular position of a combustion engine using only data representative of the angular position of a camshaft, and comprises the steps of detecting a first camshaft edge, using the expected angular position learned during a learning phase acquiring the calculated angular position of the engine, calculating a difference Dif1 between the expected angular position and the calculated angular position of the engine, comparing this difference Dif1 with a threshold value Thd1, if Dif1 < Thd1, acquiring and storing the angular position of the engine and the timestamp of the system by using or, if Dif1 > Thd1, triggering a new camshaft event at an angular position increased by a second threshold value Thd2 then, acquiring and storing a new angular position of the engine and the timestamp of the system.

Description

[0001] DESCRIPTION

[0002] METHOD FOR MONITORING AND STORING THE ANGULAR POSITION OF A HEAT ENGINE USING A CAMSHAFT SENSOR

[0003] Technical field of the invention

[0004] The invention relates to a method for monitoring and storing the angular position of a heat engine, making it possible in particular to determine the speed, or rotational speed of the engine.

[0005] More particularly, the invention relates to a method for monitoring and storing the angular position of a heat engine (in particular an internal combustion engine), operating according to a predetermined cycle, which is implemented during a degraded operating mode of the internal combustion engine.

[0006] Technical background

[0007] A thermal engine is, for example, a so-called four-stroke engine.

[0008] It has cylinders in each of which a piston moves in a reciprocating motion and this motion is transformed by connecting rods into a rotational motion of a crankshaft.

[0009] To complete a combustion cycle in a cylinder, the crankshaft makes two revolutions, or 720 degrees of rotation angle or 720°CRK. The skilled person knows how such an engine works.

[0010] For a thermal engine, an engine management process generally provides for triggering a software task called a segment, once per cylinder and per engine cycle, that is to say that during a cycle of 720°CRK of crankshaft rotation angle, there are as many segments as cylinders.

[0011] This segment is an angular appointment determined for each cylinder in a segment so that a computer can determine new setpoint values, and has time to apply them to perform associated setpoint tasks.

[0012] For an engine with four cylinders, there are therefore four rings per 720°CRK cycle, and therefore one ring every 180°CRK.

[0013] For an engine with three cylinders, there are therefore three segments per 720°CRK cycle, and therefore one segment every 240°CRK.

[0014] The angular position of the engine (expressed in °CRK modulo 720°CRK) at which, for a cylinder, the calculation of setpoint values ​​begins is called a "segment".

[0015] For an engine cycle (over two crankshaft revolutions or 720°CRK), there are as many segments as there are cylinders in the engine. At each segment (for example every 180°CRK for an engine with four in-line cylinders), the control and management system, or more specifically a computer (or ECU for Engine Control Unit) is requested to determine setpoint values. A task performed by the engine management and control system starting at a given segment is called a "segment task".

[0016] The speed, or rotational speed, must be monitored in order, for example, to avoid unexpected acceleration of the vehicle.

[0017] In fact, when the clutch that connects the engine to the transmission of torque to the vehicle's drive wheels is engaged or engaged, a connection between the thermal engine and the drive wheels is established, and an unexpected deviation in the engine's rotation speed negatively influences the vehicle's acceleration.

[0018] To perform such monitoring when the engine is synchronized, i.e. when the angular position of the crankshaft is known over the engine cycle, when the angular position of the crankshaft reaches a given value, a software segment task is activated. In a known manner, the angular position of the engine is estimated on the basis of signals representative of the angular position of the crankshaft and / or of a camshaft belonging to the distribution of the thermal engine.

[0019] For this purpose, it is known to provide the crankshaft with a crankshaft target with peripheral teeth.

[0020] A CRK crankshaft angular position sensor, which provides a crankshaft signal, is placed opposite the target and detects the passage of each tooth of the target. The signal generated by the sensor is an electrical signal whose amplitude varies according to the passage of the tooth. Analysis of this signal thus makes it possible to detect tooth edges. Each edge is thus representative of the profile of the target seen by the sensor. The sensor thus detects each passage of a rising edge or a falling edge of each tooth.

[0021] Similarly, it is known to provide the camshaft with a target with peripheral teeth.

[0022] A camshaft angular position sensor (CAM), which provides a camshaft signal, is placed opposite the target and detects the passage of each tooth of the target. The CAM sensor thus detects each passage of an active tooth edge, also called a camshaft edge or cam edge, and produces a corresponding signal. The sensor thus detects each passage of a rising or falling edge of each tooth.

[0023] A camshaft is driven by the crankshaft through a 1 / 2 ratio reduction gear.

[0024] Of course, the number of fronts can vary depending on the number of teeth on the camshaft target used.

[0025] It is known, during the first kilometers traveled by the motor vehicle, to carry out a phase or step of learning the positioning of the rising edges and falling edges of the camshaft signal in reference to the angular distance of the crankshaft target.

[0026] Alternatively, the learning step is carried out in the factory during assembly of the motor vehicle. Advantageously, the positioning relative to the crankshaft target of the rising and falling edges of the camshaft signal is stored in storage or memorization means.

[0027] For example, when the vehicle completes its first kilometers, the learning phase consists of identifying, and memorizing in a dedicated memory, the positioning of the rising edges and falling edges of the camshaft signal according to the crankshaft target.

[0028] Alternatively, an interpolation, and for example an average, of the positioning of the rising and falling edges of the first camshaft signal is carried out during several engine cycles.

[0029] In the event of a failure, for example, of the crankshaft sensor, when the signal from the CRK crankshaft sensor is absent, manufacturers have developed an operating mode for the internal combustion engine called "Limp home mode". This operating mode uses information from the CAM sensor to replace the CRK sensor.

[0030] Calculating Rated Engine Speed ​​Using Crankshaft CRK Sensor

[0031] The rotation speed, or N speed, of the engine is expressed in number of revolutions per minute (rpm).

[0032] When a segment is activated, the timestamp of the crankshaft edge used is stored and the time, or duration, T elapsed between the edges used to generate the current segment and previous segments is calculated.

[0033] The angle, or length, between the last segment and the current segment is a constant value given by the engine (Length = 720°CRK / number of cylinders; for example, for a four-cylinder engine Length=180°).

[0034] The calculated value of the engine speed N is then calculated using the following formula in which the time T is expressed in seconds.

[0035] Engine speed calculation monitoring

[0036] When this segment task is activated, data including the estimated angular position of the motor and the timestamp are acquired and stored.

[0037] The difference with similar data from the previous segment is calculated.

[0038] PosnEngDifMon is the variation of the angular position of the motor when two consecutive calculations of this speed are carried out, and

[0039] TiSegMon is the value of the time elapsed between the two timestamps.

[0040] The PosnEngDifMon value is therefore re-estimated during each segment from the estimated engine position when the task is actually executed. The engine speed monitoring NEngMdIMon value is calculated using the following formula:

[0041] > > 1 PosnEngDifMon

[0042] NEngMdlMon[l / s] = -

[0043] 2 x TT TiSegMon[s]

[0044] If the two calculated speeds differ too much, an error is triggered.

[0045] The invention aims to enable reliable and continuous monitoring of the engine speed when the signal from the CRK crankshaft sensor is absent, for example in the event of a crankshaft sensor failure.

[0046] Summary of the invention

[0047] The invention proposes a method for monitoring and storing the angular position of a heat engine which is implemented during a degraded operating mode of the heat engine using only data representative of the angular position of a camshaft driven in rotation synchronously by a crankshaft of the engine, said data being provided by a camshaft sensor making it possible to detect successive edges of a target linked in rotation to said camshaft, the method comprising the successive steps consisting of:

[0048] - E1) detect a first front of the camshaft;

[0049] - E2) determining the index of said first front of the camshaft;

[0050] - E3) use the expected angular position (PosnCamLearn), learned during a learning phase of the positioning of the rising edges and falling edges of the camshaft signal, provided by the camshaft sensor, with reference to the angular position of the crankshaft, of said first indexed edge of the camshaft;

[0051] - E4) from historical data, acquire the calculated angular position (PosnCamAcq) of the motor;

[0052] - E5) calculate a first difference Dif1 between the expected angular position (PosnCamLearn) of the first indexed front of the camshaft and the calculated angular position (PosnCamAcq) of the engine;

[0053] - E6) compare the first difference Dif1 with a first threshold value Thd1;

[0054] - E61) if Dif1 < Thd1, acquire and store the angular position of the engine and the time stamp of the system using a camshaft event activated by said first indexed edge of the camshaft; or

[0055] - E62) if Dif1 > Thd1:

[0056] --E621) activate a new camshaft event at an angular position equal to the expected angular position (PosnCamLearn) of said first indexed camshaft edge increased by a second threshold value Thd2; then

[0057] --E622) acquire and store a new motor angular position (PosnCamTrig) and the system timestamp.

[0058] According to other characteristics of the process:

[0059] - when the new camshaft event is activated, said step E62 further consists of:

[0060] --E623) calculate a second difference Dif2 between the new calculated angular position (PosnCamTrig) of the engine and the expected angular position (PosnCamLearn) of the first indexed front of the camshaft; then

[0061] -- E624) compare the second difference Dif2 with a second threshold value Th2 for: — E6241) if Dif2 < ThD2, acquire and store the new angular position of the motor (PosnCamTrig) and the system timestamp; or

[0062] — E842) if Dif2 > Thd2, compare the second difference Dif2 with a third threshold value Thd3 strictly greater than the second threshold value Thd2 to, if Dif2 < Thd3, acquire and store the new angular position of the engine (PosnCamTrig) and the system time stamp or, if Dif2 >= Thd3 acquire and store another new expected angular position of the engine (PosnCamLearn) and the system time stamp upon detection of a following cam edge of the camshaft;

[0063] - said next camshaft front is the camshaft front following said first camshaft front;

[0064] - said first threshold value Thd1 is less than or equal to three degrees of angle;

[0065] - said second threshold value Thd2 is less than or equal to one degree of angle;

[0066] - said third threshold value Thd3 is less than or equal to two degrees of angle.

[0067] Brief descriptions of the figures

[0068] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which reference will be made to the appended drawings in which:

[0069] [Fig .1 ] - Figure 1 is a schematic diagram showing an example of offsets of the generated segment triggers relative to the actual angular positions of the motor;

[0070] [Fig.2] - Figure 2 is a diagram illustrating an example of differences in positions or offsets between the values ​​seen and the actual values ​​of the positions of the cam fronts; [Fig.3] - Figure 3 is a diagram illustrating an incorrect positioning of the camshaft fronts;

[0071] [Fig .4] - Figure 4 is a diagram detail illustrating the calculated angular position and the acquired angular position of the motor;

[0072] [Fig.5] - Figure 5 is another diagram detail illustrating the calculated angular position and the acquired angular position of the motor; [Fig.6] - Figure 6 is a diagram detail illustrating three different interpolation hypotheses in a new CAM segment;

[0073] [Fig.7A] - Figure A7 is a detail of a diagram illustrating an example of a discrepancy between acquired value and estimated value;

[0074] [Fig.7B] - Figure B7 is an enlarged view of the detail circled in Figure 7A;

[0075] [Fig.8] - Figure 8 is a diagram illustrating an example of erroneous estimation of the segment trigger;

[0076] [Fig.9] - Figure 9 is a partial flowchart illustrating certain main steps and sub-steps of the method according to the invention.

[0077] Detailed description of the invention

[0078] In the following description, identical, similar or analogous elements will be designated by the same reference.

[0079] Engine speed monitoring in limp mode (when the CRK sensor is faulty or not transmitting information / signals to the system)

[0080] In the case of a so-called variable valve timing engine, when the variable valve timing is in the locked position and the signal provided by the CRK crankshaft sensor is available, the angular position of the successive edges of the camshaft is learned in order to precisely know each absolute angular position of the different edges of the camshaft.

[0081] If the crankshaft CRK sensor is faulty, the angular position should be able to be determined based on the camshaft angular position information or data provided by the camshaft CAM sensor.

[0082] In a VVT engine, if an error is detected on the signal representing the angular position of the crankshaft, the camshaft returns to the reference position.

[0083] Segment triggering is based on the engine angular position estimated using the signal representing the camshaft angular position.

[0084] Sometimes, during very rapid acceleration or deceleration, the motor angular position is not accurate and the segment trigger is generated far from the actual motor angular position at which it should have been.

[0085] This is illustrated schematically in Figure 1, where the abscissa indicates the angular position of the crankshaft over a complete 720° cycle and the ordinate indicates the trigger times in seconds. The triggers of the segments TDCO, TDC1, TDC2, TDC3 have been surrounded by ellipses, which are angularly offset, and progressively more and more, relative to the associated actual angular positions of the engine.

[0086] For a constant rotational speed, instead of being equidistant in time, the segments are not spaced regularly in time. Current control strategies implemented by a management computer of an internal combustion engine operating according to a predetermined cycle generate segment tasks when the estimated angular position of the engine reaches expected associated values.

[0087] But because estimates of the engine's angular positions can be wrong, the segments can be mislocated, and this results in poor engine speed monitoring.

[0088] In Figure 2, the differences in positions or offsets between the values ​​seen and the actual values ​​of the positions of the camshaft fronts are represented on the abscissa in degrees of angle and on the ordinate in degrees of angle.

[0089] In the crankshaft angular position error limitation mode, current strategies are not robust to high accelerations and some monitoring errors may occur.

[0090] A monitoring problem can then lead to the replacement of the computer or controller or control unit, which is desirable to avoid.

[0091] The example shown in Figure 3 shows poor location of the camshaft fronts.

[0092] Even during strong engine acceleration, the acceleration between two camshaft fronts can decrease (compression phase of a cylinder), which leads to an erroneous extrapolation of the position.

[0093] In case of combustion, regardless of engine speed, regardless of the condition of the crankshaft CRK sensor, angular velocity monitoring must be performed correctly.

[0094] The invention also aims to make monitoring more robust and less dependent on the component used to estimate the angular position of the motor.

[0095] In fact, the segment speed monitoring is performed at the segment event, which is angularly dependent.

[0096] If a problem appeared in this component, the segment would no longer be of the correct duration and therefore neither would the monitoring speed.

[0097] Definitions:

[0098] PosnCamLearn = Expected angular position learned during the learning phase of the positioning of the rising and falling edges of the camshaft signal

[0099] PosnCamAcq = Calculated angular position (Acquired by calculation) of the engine when the camshaft front is detected.

[0100] PosnCamTrig = Calculated angular position of the engine when the software task triggered by the detection of a new camshaft front is executed;

[0101] PosnCamAcq = Read angular position of the camshaft.

[0102] The invention comprises the following steps:

[0103] Step A

[0104] When the motor angular position is estimated between cam edges from the CAM sensor, it is always necessary to limit the motor angular position to a value just below the next learned cam edge angular position.

[0105] In other words, the angular position of the motor can never be calculated after the angular position of the next cam edge; that is: Angular position of the motor < PosnCamLearn .

[0106] If the angular position of the engine has been underestimated, the gap to be covered when receiving the cam front can be significant.

[0107] If the motor angular position has been overestimated, the motor angular position will be saturated at the value just before the exact angular position of the next received cam edge.

[0108] Step B

[0109] When a new cam front is received, the calculated angular position of the motor is stored, i.e.:

[0110] Angular position of the motor = PosnCamAcq , and the difference Dif1 (which is strictly positive following the limitation of Step A) between the calculated angular position and the acquired angular position is calculated:

[0111] Dif1 = PosnCamLearn - PosnCamAcq.

[0112] Sub-step B1

[0113] A comparison of the difference Dif1 is made with a first threshold value Thd 1 , making it possible to ensure that the angular position at which the time stamp and the acquisition of the angular position of the motor are plausible.

[0114] As can be seen in Figure 4, if the difference Dif1 is lower than a threshold Thd 1 (for example equal to 3°CRK), the acquisition of the angular position of the motor and the time stamp are immediately carried out.

[0115] Since it is certain that the calculated angular position of the motor is close to the actual angular position of the motor (because Dif1 is less than 3°CRK and a new cam edge is received), the acquisition of the timestamp / calculated angular position is performed by a

[0116] Existing camshaft SW “trigger” (Which is a software tool managed by the ECU operating system), a delay related to this processing will be applied.

[0117] When this trigger is actually applied, the actual angular position of the motor will therefore be closer to the actual angular position.

[0118] Sub-step B2

[0119] As can be seen in Figure 5, if the difference Dif 1 is greater than a threshold Thd 1 (for example equal to 3°CRK), a request to generate a new “confirmed edge received” trigger is made.

[0120] The request for generation of this trigger must be made after the planned CAM angular position, i.e. at: PosnCamLearn) + threshold (Thd2, for example equal to 1°).

[0121] When this trigger is executed, the acquisition of the angular position and timestamp is performed.

[0122] This new SW triggering of the camshaft is performed just after receiving the camshaft front. When this triggering is performed, the difference between the actual angular position of the engine and the calculated one must be reduced to a very low value (Close to 1 °CRK, given by the value of the threshold Thd2).

[0123] To confirm this, the calculated angular position of the motor is stored; either:

[0124] PosnCamTrig= Angular position of the motor and the difference Dif2 (which is strictly positive) between the calculated angular position and the expected angular position when the cam front was received is calculated; i.e.:

[0125] Dif2 = PosnCamTrig - PosnCamLearn.

[0126] This value should be close to 1° if the new calculated angular position is correct.

[0127] The example shown in Figure 6 shows the three different interpolation assumptions in the new CAM segment.

[0128] Hypothesis 1 is a correct estimate of engine speed.

[0129] Hypothesis 2 is a poor estimate of the angular position with too low an estimate of the slope.

[0130] Hypothesis 3 is a poor estimate of the angular position with an overly high estimate of the slope.

[0131] The acquisition used for safety of the new camshaft trigger does not pose a problem in hypotheses 1 and 2, because the angular position is close to the real angular position (The difference is less than Thd2). In hypothesis 3, the angular position could already be very far from reality.

[0132] As can be seen by referring to figures HA and HB, a new threshold Thd3 (for example equal to 2°CRK) is thus defined to distinguish hypotheses 1 and 2 from hypothesis 3.

[0133] The value of Thd3 must be strictly greater than that of Thd2. The acquisition and storage of the calculated angular position and the time stamp must be carried out if the value of Dif2 is less than the value of Thd3. This means that the actual error on the angular position is less than the value of Thd3. Since the value of Thd3 is sufficiently low, the estimation of the monitoring speed will then be correct.

[0134] If the angular position is already too large, the acquisition used for safety will not be done, but will be done at the next cam front. Indeed, as the next angular position of the camshaft will be quickly reached, the angular position will be saturated, and when the true cam front is received, the new calculated value of Dif1 will be lower than that of Thd 1. In this regard, we can refer to figures 7A and 7B.

[0135] Thd1: The 3° margin or threshold value is the (angular) length to ensure that the angular position in which the timestamp / angular position is acquired is plausible.

[0136] Thd2: The 1° margin or threshold value should be as close as possible to the time (but after the time) at which the angular position is known. Thd3: The 2° margin or threshold value ensures that 1° after the previous cam edge, the estimated angular position is still plausible.

[0137] The combination of the two margins or threshold values ​​Thd2 and Thd3 results in a low angular position error for all cam edges; the measurement error is thus reduced.

[0138] If a value does not seem plausible, it is rejected.

[0139] Advantageously, this mechanism guarantees that only one sample will be rejected. In addition, the speed used for safety will always be calculated with a longer cam segment. Thus, the speed and its variation remain plausible.

[0140] The speed is always calculated using consistent data and therefore the calculated speed is always plausible.

[0141] Indeed, the determination of the pair of quantities used for the calculation of the monitored speed [Engine position, timestamp of the present moment] is always consistent, because the described principle ensures that the engine position used in the calculation is always very close to a known value, which is the actual position of reception of the camshaft target edge. The calculation of the monitored speed can always be carried out at the segment position, even if this position is not precise, because the information used for this calculation is always consistent because it was previously determined close to the reference position.

[0142] This proposal reduces the negative effects of engine angular position estimation. Indeed, if the engine calculation is misestimated between edges, the engine angular position is wrong when the new camshaft edge is received.

[0143] If the front is received earlier than expected, the motor angular position has been underestimated and the motor angular position is quickly updated to return to the correct position.

[0144] If the underestimation was too large, generating the new 1°CRK trigger after receiving the camshaft front then makes the position estimate close to reality.

[0145] If the front is received later than expected, the engine angular position has been overestimated and the engine angular position is saturated just above the theoretical angular position of the next camshaft front until it is received. Triggering then only takes place when the new camshaft front is received. The estimated angular position at this time is therefore close to reality.

[0146] The segment trigger can still be used for monitoring speed display / calculation, even if the actual angular position of this trigger is not correct.

[0147] The example shown in Figure 8 shows an example of a segment trigger misestimation.

[0148] For example, the 546° segment is generated upon receipt of edge #5, while the actual angular position of the motor is equal to 603° (with a 60° delay). The segment trigger is generated while the calculation of the angular position of the motor is rapidly updated.

[0149] In the case of a return to normal, the engine speed is actually monitored. In other words, the speed is monitored using the system clock and time and the angular position of the engine.

[0150] Such monitoring is different from nominal cam speed monitoring which uses the time between camshaft edges and the known angular position between the edges).

[0151] The main advantage of this process is to give the system a chance to regain the correct engine speed, even if the engine angular position is not correct.

Claims

CLAIMS 1. Method for monitoring and storing the angular position of a heat engine which is implemented during a degraded operating mode of the heat engine using only data representative of the angular position of a camshaft driven in rotation synchronously by a crankshaft of the engine, said data being provided by a camshaft sensor making it possible to detect successive edges of a target linked in rotation to said camshaft, the method comprising the successive steps consisting of: - E1) detect a first front of the camshaft; - E2) determine the index of said first front of the camshaft; - E3) use the expected angular position (PosnCamLearn), learned during a learning phase of the positioning of the rising edges and falling edges of the camshaft signal, provided by the camshaft sensor, with reference to the angular position of the crankshaft, of said first indexed edge of the camshaft; - E4) from historical data, acquire the calculated angular position (PosnCamAcq) of the motor; - E5) calculate a first difference Dif1 between the expected angular position (PosnCamLearn) of the first indexed front of the camshaft and the calculated angular position (PosnCamAcq) of the engine; - E6) compare the first difference Dif1 with a first threshold value Thd1; - E61) if Dif1 < Thd1, acquire and store the angular position of the engine and the time stamp of the system using a camshaft event activated by said first indexed edge of the camshaft; or - E62) if Dif1 > Thd1: --E621) activate a new camshaft event at an angular position equal to the expected angular position (PosnCamLearn) of said first indexed camshaft edge increased by a second threshold value Thd2; then --E622) acquiring and storing a new engine angular position (PosnCamTrig) and the system timestamp and in that when the new camshaft event is activated, said step E62 further consists of: --E623) calculate a second difference Dif2 between the new calculated angular position (PosnCamTrig) of the engine and the expected angular position (PosnCamLearn) of the first indexed front of the camshaft; then -- E624) compare the second difference Dif2 with a second threshold value Th2 for: — E6241) if Dif2 < ThD2, acquire and store the new angular position of the motor (PosnCamTrig) and the system timestamp; or — E842) if Dif2 > Thd2, compare the second difference Dif2 with a third threshold value Thd3 strictly greater than the second threshold value Thd2 to, if Dif2 < Thd3, acquire and store the new angular position of the motor (PosnCamTrig) and the system timestamp or, if Dif2 >= Thd3 acquire and store another new expected angular position of the motor (PosnCamLearn) and the system timestamp when detecting a following cam edge of the camshaft.

2. Method according to claim 1, characterized in that said next cam front of the camshaft is the cam front following said first cam front.

3. Method according to any one of claims 1 to 2, characterized in that said first threshold value Thd1 is less than or equal to three degrees of angle.

4. Method according to any one of claims 1 to 3, characterized in that said second threshold value Thd2 is less than or equal to one degree of angle.

5. Method according to one of the preceding claims, characterized in that said third threshold value Thd3 is less than or equal to two degrees of angle.

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