Method for protecting a dual mass flywheel, by detecting that it is entering into resonance when the engine is running

Abstract

A method for protecting a dual mass flywheel DMF, by detecting, when the engine in running, that the DMF is entering into resonance, the DMF being arranged between an internal combustion engine and a gearbox of a vehicle, comprising the following steps: • Determining the average rotational speed (Vvil.sub.moy) of the crankshaft, over time, over a predetermined given period, as a first parameter constituting a risk of the DMF entering into resonance, • Measuring the maximum instantaneous rotational speed and the minimum instantaneous rotational speed of the crankshaft, the difference defining the maximum amplitude (Amp.sub.Vvil) of the rotational oscillations of the crankshaft, over the period, as a second parameter constituting a risk of the DMF entering into resonance, • Detecting when the DMF is entering into resonance from a determined combination of values of the first and second parameters, over the period, • limiting or cutting off the fuel injection in the cylinders after said detection.

Claims

1. A method for protecting a dual mass flywheel by detecting, when the engine is running, that the dual mass flywheel is entering into resonance, this flywheel being positioned between an internal combustion engine and a gearbox of a vehicle, the method comprising: determining a mean rotational speed of the crankshaft, over the course of time over a predetermined given period, as being a first parameter involved in a risk of the dual mass flywheel entering into resonance, measuring a maximum instantaneous rotational speed and a minimum instantaneous rotational speed of the crankshaft, using the difference to define the maximum amplitude of fluctuations in the rotation of the crankshaft, over said predetermined given period, as being a second parameter involved in a risk of the dual mass flywheel entering into resonance, detecting that the dual mass flywheel has entered into resonance from a determined combination of values of said first and second parameters, over said predetermined given period, wherein the dual mass flywheel is detected to have entered into resonance when the combination of values of said first and second parameters are as follows: said mean rotational speed of the crankshaft is between a predetermined maximum increase value and a predetermined maximum decrease value on each side of a stable mean speed value, said stable mean speed value is below or equal to a first predetermined threshold; and said maximum amplitude of the fluctuations in the rotation of the crankshaft is higher than or equal to a second predetermined threshold; and limiting or cutting off an injection of fuel into cylinders of the engine after having detected that the dual mass flywheel has entered into resonance.

2. The method as claimed in claim 1, wherein said predetermined given period is between 0.5 s and 2 s.

3. The method as claimed in claim 1, wherein said predetermined given period is between 1 s and 2 s.

4. A device for protecting a dual mass flywheel by detecting, when the engine is running, that the dual mass flywheel is entering into resonance, this flywheel being positioned between an internal combustion engine and a gearbox of a vehicle, comprising: means for determining a mean rotational speed of the crankshaft, over the course of time over a predetermined given period, as being a first parameter involved in a risk of the dual mass flywheel entering into resonance, means for measuring a maximum instantaneous rotational speed and a minimum instantaneous rotational speed of the crankshaft, using the difference to define the maximum amplitude of fluctuations in the rotation of the crankshaft, over said predetermined given period, as being a second parameter involved in a risk of the dual mass flywheel entering into resonance, means for detecting that the dual mass flywheel has entered into resonance from a determined combination of values of said first and second parameters, over said predetermined given period, wherein the means for detecting detects that the dual mass flywheel has entered into resonance when the combination of values of said first and second parameters are as follows: said mean rotational speed of the crankshaft is between a predetermined maximum increase value and a predetermined maximum decrease value on each side of a stable mean speed value, said stable mean speed value is below or equal to a first predetermined threshold; and said maximum amplitude of the fluctuations in the rotation of the crankshaft is higher than or equal to a second predetermined threshold; and means for limiting or cutting off an injection of fuel into cylinders of the engine after having detected that the dual mass flywheel has entered into resonance.

5. The device as claimed in claim 4, wherein said means for determining the mean rotational speed of the crankshaft, said means for measuring the maximum instantaneous rotational speed and the minimum instantaneous rotational speed of the crankshaft, using the difference to define the maximum amplitude of the fluctuations in the rotation of the crankshaft, and said means for detecting that the dual mass flywheel has entered into resonance from a determined combination of values of said first and second parameters, over said predetermined given period, said means for limiting or cutting off an injection of fuel into the cylinders after having detected that the dual mass flywheel has entered into resonance, comprise a crankshaft position detector made up of a plurality of teeth making it possible to determine the rotational speed of the crankshaft, tooth by tooth, and an engine control unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram of an example of a curve of the rotational speed of the crankshaft according to one example of a method according to an aspect of the invention for protecting a dual mass crankshaft by detecting that it has gone into resonance while the engine is running,

(2) FIG. 2 is a flow diagram of an example of a method according to an aspect of the invention for protecting a dual mass crankshaft by detecting that it has gone into resonance while the engine is running,

(3) FIG. 3 is a diagram of one example of a curve of the rotational speed of the crankshaft during an engine start,

(4) FIG. 4 is a diagram of one example of a curve of the rotational speed of the crankshaft during return of the engine to low-idle speed.

(5) FIG. 5 is a basic diagram of one exemplary embodiment of a device according to an aspect of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) The diagram in FIG. 1 shows the evolution of the curve of the crankshaft speed Vvil or engine speed of a vehicle, measured over the course of time, for example for a vehicle moving along under the action of a multi-cylinder combustion engine. The abscissa axis bears a scale of time t in seconds (s), and the ordinate axis bears a scale of engine speed V or crankshaft rotational speed in revolutions per minute (rpm). The low-idle speed has been indicated by a defined horizontal mark predetermined by the engine control unit (not depicted) at 800 rpm in this instance.

(7) In the engine example given in FIG. 1, the crankshaft speed illustrated by the curve Vvil passes, over the course of time, over a period of around half a second corresponding to half the length of the abscissa axis depicted, from a speed of around 2000 rpm to a mean speed of the order of 500 to 600 rpm, representing, for example, a stalling phase, or a decrease in engine speed in an underspeed zone, the vehicle running at very low speed with a gear, for example fifth gear, engaged.

(8) The curve Vvil of crankshaft speed is obtained by a crankshaft position toothed sensor comprising for example 60 teeth making it possible to calculate the instantaneous speed of the crankshaft tooth by tooth, in the known way, for example by measuring the angular displacement of the sensor between two signals given by the passing of two successive teeth past the sensor, and by measuring the time elapsed between these two signals. Thus, the speed curve shows fluctuations in engine speed over the course of time in a predetermined given period, illustrating accelerations in speed during combustions in the cylinders, and decelerations between combustions.

(9) Simultaneously with measuring the instantaneous speed tooth by tooth using the sensor, the engine control unit calculates the mean rotational speed of the crankshaft, likewise in the known way, by averaging the instantaneous speed over a predetermined given period.

(10) The curve Vvil illustrated in FIG. 1 therefore has a first phase of decrease in the mean rotational speed of the crankshaft, passing from a mean speed of around 2000 rpm to a mean speed of the order of 500 to 600 rpm, namely below the mean low-idle speed Vvil.sub.ral set at 800 rpm.

(11) By studying the evolution in the rotational speed Vvil over the time period [0, t1] in FIG. 1, it is found that there is a fairly steeply decreasing mean speed with, at the same time, significant and increasing maximum amplitudes of fluctuation. According to an aspect of the invention, because the mean speed is steeply decreasing, there are no grounds for detecting that the DMF is entering into resonance, because the engine could be in a stopping phase. Over the period P.sub.rés which follows on from the instant t1 and is comprised between the instants t1 and t2 as depicted, having a duration of around 0.5 s, it is found that the mean speed calculated from the rotational speed Vvil of the crankshaft has stabilized or near-stabilized, in this example at a speed of the order of 500 to 600 rpm and that the maximum amplitude Amp.sub.Vvil of the fluctuations in engine speed is still high.

(12) What is meant here by the mean rotational speed of the crankshaft being near-stabilized is a mean speed which may potentially vary within a permitted range of variation, which is small about a stabilized speed. For preference, the permitted range of variation in mean speed is of the order of 200 rpm, more preferably of the order of 100 rpm.

(13) Thus, according to an aspect of the invention: first of all, the mean rotational speed Vvil.sub.moy of the crankshaft has been determined over the course of time over a predetermined period P.sub.rés, for example greater than 0.5 s in FIG. 1, comprised between t1 and t2, as being a first parameter involved in a risk of the dual mass flywheel entering into resonance, this mean speed Vvil.sub.moy advantageously adopting: a value comprised between a predetermined maximum increase value and a predetermined maximum decrease value, distributed on either side of a stable mean speed value Vvil.sub.moy, in this example a stabilized mean speed Vvil.sub.moy of the order of 600 rpm with a permissible range of variation about the stabilized speed for example of the order of 100 rpm, and said stable mean speed value being below or equal to a predetermined threshold S.sub.Vvilmoyrés, in this example the threshold S.sub.Vvilmoyrés being fixed at the mean low-idle speed Vvil.sub.ral of 800 rpm, and the stabilized mean speed Vvil.sub.moy over the period comprised between t1 and t2 being of the order of 600 rpm, secondly, the instantaneous maximum rotational speed and the instantaneous minimum rotational speed of the crankshaft have been determined, the difference between these determining the maximum amplitude Amp.sub.Vvil of the fluctuations in rotation of the crankshaft over the same predetermined given period P.sub.rés, namely the period of time comprised between t1 and t2, as being a second parameter involved in the risk of the dual mass flywheel entering into resonance; the maximum amplitude Amp.sub.Vvil of the fluctuations in the rotation of the crankshaft adopting, in this example, a value higher than or equal to a predetermined threshold S.sub.AmopVvilrés, for example a maximum amplitude higher than or equal to 100 rpm, preferably higher than or equal to 200 rpm, from a determined combination of values of the first and second parameters, over this predetermined given period P.sub.rés, it has thus been detected that the dual mass flywheel has entered into resonance.

(14) According to FIG. 1, once the diagnosis that the DMF has entered into resonance has been made, injection can be limited or cut off in any known way using the engine control unit, in order to get out of this resonance situation, in the case of a non-hybrid vehicle.

(15) One example of a method according to an aspect of the invention will now be described using the flow diagram of FIG. 2.

(16) With a view to limiting the use of computation means and memory space in the engine control unit, activation of the method for detecting that the DMF has entered into resonance may advantageously be limited. For example, the method may be activated only when the engine is operating below a given mean rotational speed threshold Seuil.sub.survVvil. This monitoring threshold Seuil.sub.survVvil is defined as being the speed above which there is no risk of DMF resonance. The threshold Seuil.sub.survVvil can be established by calibration for each vehicle or defined in general as a speed that is perhaps higher but more generic, for example a speed of the order of 2000 rpm.

(17) In step 10 in FIG. 2, the engine control unit continuously calculates the mean rotational speed Vvil.sub.moy of the crankshaft and moves on to the next step 20 when this mean rotational speed Vvil.sub.moy of the crankshaft is below the threshold speed Seuil.sub.survVvil set, for example, at 2000 rpm.

(18) In steps 20 and 21 in FIG. 2, the engine control unit continuously calculates the mean rotational speed Vvil.sub.moy of the crankshaft and the maximum amplitude Amp.sub.Vvil of the fluctuations in crankshaft rotation, respectively.

(19) The critical stabilized mean speed Vvil.sub.moy, namely below or equal to the speed threshold S.sub.Vvilmoyrés, is dependent on the gearbox gear ratio engaged, and is therefore established by calibration for each gearbox ratio; if no gear is engaged, a critical stabilized mean speed value Vvil.sub.moy is for example of the order of 600 rpm, in a range of variation comprised between 100 and 200 rpm.

(20) The engine control unit has in memory the current period P=[t1, t2], for example a period comprised between 0.5 and 2 seconds, preferably between 1 and 2 seconds of stability, which serves as a calculation basis for detecting that the DMF has gone into resonance, at the end of which period the control unit proceeds with continuously evaluating the combination of the first and second parameters, the mean rotational speed Vvil.sub.moy of the crankshaft and the maximum amplitude Amp.sub.Vvil of the fluctuations in crankshaft rotation, this reference to the monitoring period being indicated by step 22 in FIG. 2.

(21) During step 30, over a current period P=[t1, t2], the engine control unit monitors the evolution in mean speed as indicated above in order to detect stability thereof, likewise as indicated above, and also compares the value of this mean rotational speed Vvil.sub.moy of the crankshaft against the speed threshold S.sub.Vvilmoyrés, and compares the calculated maximum amplitude Amp.sub.Vvil of the fluctuations in crankshaft rotation against the predetermined threshold S.sub.AmpVvilrés, these operations also being carried out in the memory of the ECU and: if the mean rotational speed Vvil.sub.moy of the crankshaft is stable or near-stable and also below or equal to the speed threshold S.sub.Vvilmoyrés, and if the calculated maximum amplitude Amp.sub.Vvil of the fluctuations in the rotation of the crankshaft is above or equal to the predetermined threshold S.sub.AmpVvilrés, then in step 50 in FIG. 2, the engine control unit limits or cuts off the injection of fuel to the cylinders; the method then returns to step 10 described above.

(22) If the answer at step 30 is in the negative, the engine control unit proceeds to a step 40 as follows: if the mean rotational speed Vvil.sub.moy of the crankshaft is not stable or near-stable, or if the mean rotational speed Vvil.sub.moy of the crankshaft is above the speed threshold S.sub.Vvilmoyrés, or if the calculated maximum amplitude Amp.sub.Vvil of the fluctuations in the rotation of the crankshaft is below the predetermined threshold S.sub.AmpVvilrés, then during a step 60, the engine control unit proceeds to increase the torque up to the limit of the torque demanded by the driver; the method then returns to step 10 described above.

(23) If the answer at step 40 is in the negative, the method then returns to step 10 described above.

(24) FIG. 3, which shows an example of how the rotational speed of the crankshaft evolves during an engine start, must not lead to a diagnosis that the DMF has entered into resonance, according to the method described in FIG. 2, as explained hereinafter.

(25) The abscissa and ordinate axes in this FIG. 3 are identical to those of FIG. 1 and the same references as those used in FIG. 1 indicate similar means.

(26) In the period P=[t1, t2] the engine control unit logs a steep increase in the mean rotational speed Vvil.sub.moy of the crankshaft, followed, after the instant t2, by this mean speed stabilizing around a speed of 800 rpm, representing the engine low-idle speed, with an attenuation in the fluctuations in the rotation of the crankshaft. During the steep increase in the mean rotational speed Vvil.sub.moy of the crankshaft in the period P, the maximum amplitude Amp.sub.Vvil of the fluctuations in the rotation of the crankshaft is high and for example exceeds the threshold S.sub.AmpVvilrés used in the engine control unit. Nevertheless, the second parameter which consists of the evolution in mean speed Vvil.sub.moy over the period P does not demonstrate any stability. As a result, step 30 according to the flow diagram of FIG. 2 is not satisfied, and the method in this case passes on to step 40, which is a step that is the reverse of step 30.

(27) In the example of FIG. 3, step 40 is satisfied because, over the period P considered, despite a maximum amplitude Amp.sub.Vvil above the threshold S.sub.AmpVvilrés, the mean speed Vvil.sub.moy over the period P is not stable, this second parameter being alternative of the first in step 40. The method thus in this case passes on to step 60, which consists in increasing the engine torque within the limit of the torque demanded by the driver.

(28) FIG. 4, which shows an example of how the rotational speed of the crankshaft evolves during a return to engine low-idle speed, must not lead to a diagnosis that the DMF has entered into resonance, according to the method described in FIG. 2, as explained hereinafter.

(29) The abscissa and ordinate axes in this FIG. 4 are identical to those of FIG. 1 and the same references as those used in FIG. 1 indicate similar means.

(30) In the period P=[t1, t2] comprised between the instants t1 and t2 as indicated, the engine control unit logs stability in the mean rotational speed Vvil.sub.moy of the crankshaft about a speed of 800 rpm which represents the low-idle speed of the engine, this stability being accompanied by fluctuations in engine speed which are of low amplitude Amp.sub.Vvil. Despite the stability of the mean speed Vvil.sub.moy, the engine control unit therefore logs, in that same period P, a maximum amplitude Amp.sub.Vvil that is below the critical resonance threshold S.sub.AmpVvilrés. As a result, step 30 according to the flow diagram of FIG. 2 is not satisfied, and the method in this case passes on to step 40.

(31) In the example of FIG. 4, step 40 is satisfied because, over the period P considered, the maximum amplitude Amp.sub.Vvil is below the threshold S.sub.AmpVvilrés. The method thus in this case passes on to step 60, which consists in increasing the engine torque within the limit of the torque demanded by the driver.

(32) In FIG. 4, before the instant t1 of entering the period P, the engine control unit logs a steep decrease in the mean crankshaft speed accompanied by high-amplitude fluctuations in crankshaft rotation, as shown, and does not detect entry into resonance because the mean speed is not stable or near-stable as explained in connection with the example of FIG. 3.

(33) FIG. 5 depicts an example of a layout of a device for protecting a dual mass flywheel by detecting, when the engine is running, that the dual mass flywheel is entering into resonance, this flywheel being positioned between an internal combustion engine 3 and a gearbox 4 of a vehicle 5, comprising: means 1, 2 for determining the mean rotational speed of the crankshaft, over the course of time, over a predetermined given period, as being a second parameter involved in a risk of the dual mass flywheel wheel entering into resonance, taken from a crankshaft position sensor 1, and an engine control unit 2 processing the signal from the position sensor 1, as explained above in the known way, means 1, 2 for measuring the maximum instantaneous rotational speed and the minimum instantaneous rotational speed of the crankshaft, using the difference to define the maximum amplitude of the fluctuations in the rotation of the crankshaft, over the predetermined given period, as being a first parameter involved in a risk of the dual mass flywheel DMF entering into resonance, means 1, 2 for detecting that the dual mass flywheel has entered into resonance from a determined combination of values of said first and second parameters, over said predetermined given period, means 2 for limiting or cutting off an injection of fuel into the cylinders after having detected that the dual mass flywheel has entered into resonance.

(34) As indicated in FIG. 5, the means for determining the mean rotational speed of the crankshaft, the means for measuring the maximum instantaneous rotational speed and the minimum instantaneous rotational speed of the crankshaft, using the difference to define the maximum amplitude of the fluctuations in the rotation of the crankshaft, and the means for detecting that the dual mass flywheel DMF has entered into resonance from a determined combination of values of said first and second parameters, over the predetermined given period P, the means for limiting or cutting off an injection of fuel into the cylinders after having detected that the dual mass flywheel has entered into resonance, comprise a crankshaft position detector 1 made up of a plurality of teeth making it possible to determine the rotational speed tooth by tooth, and an engine control unit 2 of known type, for example not conventionally fitted to an internal combustion engine, and implemented using software according to a method for example as described hereinabove with the aid of FIG. 2.