FR3051226B1 - METHOD FOR CONTROLLING AT LEAST ONE DEHASTER OF A MOTOR VEHICLE THERMAL MOTOR DURING A STOP PHASE - Google Patents

Abstract

The invention relates to a method for controlling at least one phase shifter of a camshaft of a motor vehicle engine during a stopping phase of the engine, said at least one phase shifter being, from an idle position at the beginning of the phase, placed in a position that minimizes the admission of air to the iso-pressure motor. During the engine stopping phase, said at least one phase-shifter is placed in an intermediate position between the idle position and the position that minimizes the admission of air to the engine, with in this intermediate position an increase in the air flow rate. to the engine with respect to the position minimizing the air intake, this intermediate position being maintained as long as a engine speed is above a calculated speed threshold (N_Lim), said at least one phase shifter being placed in the position that minimizes the admission of air to the engine as soon as the engine speed is below the engine speed threshold (N_Lim) calculated.

Description

METHOD FOR CONTROLLING AT LEAST ONE DEPHASER OF A MOTOR VEHICLE HEAT ENGINE DURING A STOPPING PHASE The invention relates to a method for controlling at least one phase shifter of a camshaft d 'A motor vehicle heat engine during an engine shutdown phase. Such a control method according to the invention finds a preferential but non-limiting application when associated with a motor vehicle provided with an automatic engine stop and restart system.

The invention therefore relates to the control of phase shift systems of the distribution of a heat engine. A heat engine has one or more cylinders supplied with fresh air by air flowing into the or each cylinder by an intake valve. After combustion in the cylinder, the combustion gases are evacuated by an exhaust valve.

The heat engine also includes distribution means with adjustable phase shift adapted to control the opening of said intake and exhaust valves. These distribution means include phase shifters which act on a camshaft. Piloting a heat engine is based on piloting the air and the ignition advance. This allows for example to constitute a torque reserve for the engine.

The present invention relates more particularly to the engine stopping phases. In a known manner, during a request to stop the engine, the phase shifter (s) are placed in a position which minimizes the air admitted at iso-intake pressure, for example by being the one for which the least air is admitted to iso-pressure of admission. This makes it possible to reduce an acyclic torque during stopping, therefore the jolts of the engine felt by the passengers of the motor vehicle.

A valve called a butterfly valve in an air intake line is closed as soon as one starts the shutdown because this has the effect of emptying the plenum and reducing the air admitted into each cylinder when the engine goes into the critical speed zone, generally below 500 revolutions per minute or rpm.

However, if we start from a relatively high intake pressure, the emptying of the plenum is less because the engine will not have time to empty the plenum enough before going under 500 rpm. This causes poor vibration performance to be obtained in these cases. The harmful effect is all the more visible as the level of vibrations is dispersed from one stop to another, which is the case when you know that an intake pressure at idle can easily vary from 300mbar to 700mbar according to power consumption.

Document WO-A-2015138185 describes a delayed admission camshaft phase shifter to improve the quality of combustion in an internal combustion engine associated with an automatic engine stop and restart system. According to the teaching of this document, the intake camshaft phase shifter is totally or partially delayed during an engine restart in order to control a position of the camshaft and to prevent pre-ignition. This delays a moment of spark in the first cylinder in order to delay the combustion phase setting. This delay takes place, however, at a start and not during a stop phase and this document is not concerned with a reduction in jerks during a stop phase occurring at low engine speeds.

Therefore, the problem underlying the invention is during a shutdown phase of a heat engine to reduce the jolts of the engine.

To achieve this objective, there is provided according to the invention a method for controlling at least one phase shifter of a camshaft of a thermal engine of a motor vehicle during an engine stop phase, said at least one phase shifter being, from an idle position at the start of the phase, placed in a position minimizing the admission of air to the iso-pressure motor, characterized in that, during the phase of stopping the motor, said at least one phase shifter is placed in an intermediate position between the idle position and the position minimizing the admission of air to the motor, with in this intermediate position an increase in an air flow rate to the motor relative to the position minimizing the air intake, this intermediate position being maintained as long as an engine speed is above a calculated speed threshold, said at least one phase shifter being placed in the position minimizing the air intake r to the engine as soon as the engine speed is below the calculated engine speed threshold.

The technical effect is by piloting at least one phase shifter during a stop phase of the vehicle by passing it from its idle regulation position to an intermediate position other than the position minimizing the admission of air to the engine. . Passing through this intermediate position will increase the engine air flow and improve the emptying of the plenum, especially when the idle pressure is high. When passing a critical speed threshold, the phase shifters are then tilted to their position which is most favorable to disturbance which is that which minimizes the admission of air to the motor, that is to say that which admits the less air at iso-pressure of admission. The aim here is to avoid having a high flow rate and therefore greater acyclic torques, when one is in the critical speed region of engine speed, for example less than 500 rpm. The present invention therefore allows an improvement in the benefit of reducing the shaking at standstill simply by a software modification which therefore has a low cost.

Advantageously, the placement in the intermediate position is done opposite one or more operating parameters of the engine such as an instant of request to cut off a fuel injection into the engine and / or of the ignition, a instant of actual shutdown of the injection and / or ignition, these parameters being taken with or without time delay.

Advantageously, a phase shift setpoint is issued aiming to place said at least one phase shifter in the intermediate position, this phase shift setpoint being maintained as long as the engine speed is above the calculated speed threshold.

Advantageously, a critical speed zone is defined in which, from an upper limit of this critical speed zone acting as the calculated speed threshold, said at least one phase shifter is placed in the position minimizing the air intake to the engine, the critical speed threshold being calculated according to, on the one hand, a first duration of passage of said at least one phase shifter to pass from its current intermediate position to the position minimizing air intake to the engine and, on the other hand, a second duration of reaching by the engine speed of the upper limit of the critical zone.

Advantageously, the first passage time is calculated as a function of the difference in angular position between the intermediate position and the position minimizing the admission of air to the motor divided by the angular speed of said at least one phase shifter.

Advantageously, the angular speed of said at least one phase shifter is estimated by calibration, with a specific calibration for each direction of rotation of said at least one phase shifter and an identification of the direction of rotation of said at least one phase shifter before calculation or the speed. angular of said at least one phase shifter is estimated and corrected continuously.

It is possible to select two different calibrations because a phase shifter does not necessarily have the same speed in its two directions of movement. This requires identifying the direction in which said at least one phase shifter rotates to choose the appropriate calibratable value. Alternatively, information can come from an engine control by giving an estimate of this speed and correcting the value continuously.

Advantageously, for the calculation of the second duration of reaching by the engine speed of the upper limit of the critical zone, an instantaneous speed value is noted at a last Top Dead Center of the engine passed since the start of the stop phase, then a time count is triggered from this last Top Dead Center to a new Top Dead Center coming and replacing the last Top Dead Center, the instantaneous speed value at this last Top Dead Center becoming the instantaneous speed value at the penultimate Top Dead Center, the time count giving a duration between the penultimate Top Dead Center and the last Top Dead Center and an average speed fall slope V_Chut_N is calculated according to the equation:

V_Chut_N = (NderPMH - N_penult_PMH) / t_ent_2_der_PM NderPMH being the instantaneous speed value at the last top dead center, N_penult_PMH being the instantaneous speed value at the penultimate top dead center and t_ent_2_der_PM the time between the penultimate top dead center and the last top dead center , a value of the approximate average speed current of the engine being calculated as a function of the slope of the average speed drop.

Advantageously, the value of the approximate average speed current NCour of the engine is calculated according to the following equation:

N Cour = N der PMH + V_Chut_N. t_dep_der_PMH

N der TDC being the instantaneous speed value at the last Top Dead Center, V_Chut_N the slope of the average speed drop and t_dep_der_PMH the duration since the last Top Dead Center, this value of current approximate average speed being compared to a speed forming the upper bound of the critical speed zone and an approximation of second duration t_N_Lim reached by the engine speed of the upper limit of the critical zone being calculated according to the following equation:

t_N_Lim = (N Yard - NLim) / V_Chut_N

N Cour being the value of the current approximate average speed, N Lim the upper limit and V_Chut_N the slope of the average speed fall.

Advantageously, the second duration of reaching by the engine speed of the upper limit of the critical zone is compared to the first passage duration and, if the first passage duration is greater than or equal to the second duration of attack , said at least one phase shifter is placed in the position minimizing the admission of air to the motor.

The invention also relates to a motor vehicle comprising a heat engine associated with an automatic engine stop and restart system, the engine having at least one camshaft phase shifter, characterized in that, during an engine stop phase caused by the automatic engine stop and restart system, said at least one phase shifter is controlled in accordance with such a method of controlling said at least one phase shifter.

Other characteristics, objects and advantages of the present invention will appear on reading the detailed description which follows and with regard to the appended drawings given by way of nonlimiting examples and in which:

- Figures 1a to 1e are schematic representations of a respective flow diagram of the steps of an embodiment according to the present invention of a method of controlling at least one phase shifter of a camshaft of a heat engine motor vehicle during an engine shutdown phase,

- Figures 2 and 3 are respective schematic representations of three curves of instantaneous engine speed, phase shifter setpoint and phase shifter position assuming a constant displacement speed of the phase shifter but different depending on the direction of rotation depending time during a stopping phase of the heat engine of a motor vehicle by implementing a control method according to the present invention.

It should be borne in mind that the figures are given by way of examples and are not limitative of the invention. In particular, certain steps described in the flow diagram of FIGS. 1 a to 1 e are not essential for the implementation of the control method according to the present invention.

Referring mainly to Figures 1a to 1e, the present invention relates to a method for controlling at least one phase shifter of a camshaft of a thermal engine of a motor vehicle during a stop phase of the engine. Said at least one phase shifter is, from an idle position at the start of the phase, placed in a position minimizing the admission of air to the iso-pressure motor. This position is advantageously the rest position of said at least one phase shifter and this position is generally that which will admit the least air at iso-inlet pressure.

This is done to reduce the acyclic torque during the stop, therefore the engine jolts felt by the passengers of the motor vehicle. As previously mentioned, this allows the plenum to be emptied and the air admitted to the cylinder to be reduced when the engine passes into the critical speed zone, generally at 500 rpm.

According to the invention, during the engine stop phase, said at least one phase shifter is placed in an intermediate position between the idle position and the position minimizing the admission of air to the engine, with in this position intermediate an increase in air flow to the engine relative to the position minimizing air intake.

This intermediate position is maintained as long as an engine speed is above a calculated NLim speed threshold, visible in Figure 1d. Said at least one phase shifter is placed in the position minimizing the admission of air to the engine as soon as the engine speed is lower than the engine speed threshold N Lim calculated.

Placement in the intermediate position can be done with respect to one or more operating parameters of the engine such as an instant of request to cut off a fuel injection into the engine and / or of ignition, an instant effective cut off of the injection and / or ignition, these parameters being taken with or without time delay. Placement in the intermediate position, as the first phase of the process according to the invention, can even be done in anticipation of the engine shutdown or the start of the engine shutdown phase.

Thus, the method according to the present invention can be activated when one of the control elements determines that an automatic stop phase will be initiated, for example the engine control or a control element of a stop system. and automatic starting for which the process can find a preferential but not limiting application.

An AOAInter phase shift instruction, visible in Figure 1a, can be issued to place said at least one phase shifter in the intermediate position. This AOA Inter phase shift setpoint can be maintained as long as the engine speed is above the calculated N Lim speed threshold. Said at least one phase shifter can thus be moved to a preferred angular position making it possible to increase the air flow.

It can be defined a critical speed zone in which, from an upper limit of this critical speed zone acting as calculated NLim speed threshold, said at least one phase shifter is placed in the position minimizing the air intake to the engine.

The critical speed threshold N Lim can be calculated according to, on the one hand, a first duration of passage of said at least one phase shifter to pass from its current intermediate position to the position minimizing the admission of air to the engine and , on the other hand, a second duration of reaching by the engine speed of the upper limit N Lim of the critical zone.

The critical speed threshold N Lim can therefore be calculated by comparing two signals:

- a signal determining a duration, called the first passage duration, which the phase shifter will need to pass from its current position to the rest position, and

a signal determining another duration, known as the second reaching duration, which remains at engine speed to reach the critical speed zone, that is the upper limit of this zone forming the speed limit N Lim calculated in the method according to the present invention.

A second phase of placing said at least one phase shifter in the position minimizing the air intake, is therefore launched on a very specific condition: The phase shifter must have returned to an angular position to which it admits the least. air intake pressure when the engine has reached the critical speed zone.

For simplicity, this position will be designated here as the rest position because of the application for which it was designed but in a generic way this position is not necessarily the rest position.

It will now be detailed how the first and second durations can be calculated. The first passage time can be calculated as a function of the difference in angular position between the intermediate position and the position minimizing the admission of air to the motor divided by the angular speed of said at least one phase shifter.

This first duration can be simply calculated by comparing the current position of said at least one phase shifter and the position minimizing the intake of air to the motor. By dividing this difference by the speed of the phase shifter, we obtain the first duration. The angular speed of said at least one phase shifter can be determined either by calibration or by more complex logic.

The angular speed of said at least one phase shifter can be estimated by calibration, with a specific calibration for each direction of rotation of said at least one phase shifter and an identification of the direction of rotation of said at least one phase shifter before calculation. Alternatively, the angular speed of said at least one phase shifter can be estimated and corrected continuously.

For the calculation of the second duration of reaching by the engine speed of the upper limit N Lim of the critical zone, an instantaneous speed value can be noted at a last Top Dead Center of the engine passed since the start of the stop phase. It can then be triggered by a time count from this last Top Dead Center to a new coming Top Dead Center and replacing the last Top Dead Center, the instantaneous speed value at this last Top Dead Center becoming the value of instantaneous regime at the penultimate Top Dead Center.

In what follows, it will also be used TDC or Top Dead Center. FIGS. 1a and 1b show the steps for measuring the instantaneous speed at the last TDC of compression passed since the start of the engine shutdown, hereinafter designated NderPMH, at the instant when it is passed and the step for launching d 'a time counter, hereinafter designated t_dep_der_PMH.

At this same instant, as shown in FIG. 1a, in which N denotes the instantaneous speed of the crankshaft and I TDC designates the instant of passage from a Top Dead Center, we will affect the previous value of N der TDC in a flow which records the instantaneous regime at the penultimate TDC compression passed since the start of the cut which will be called here N_penult_PMH.

As shown in Figure 1b, it is also assigned the previous value t_dep_der_PMH to a variable which will therefore designate the duration between the last two TDCs referenced t_ent_2_der_PMH. In Figure 1b, Nb_PMH_Coup designates the calculation of the number of High Dead Points spent without combustion.

As shown in FIG. 1c, the time counting gives a duration between the penultimate Top Dead Center and the last Top Dead Center and an average speed fall slope V_Shut_N is calculated according to the equation:

V_Chut_N = (N der PMH - N_penult_PMH) / t_ent_2_der_PM

NderPMH being the value of instantaneous speed at the last Top Dead Center, N_penult_PMH being the value of instantaneous speed at the penultimate Top Dead Center and t_ent_2_der_PM the time between the penultimate Top Dead Center and the last Top Dead Center, an average value of current approach of the engine being calculated as a function of the average speed fall slope V_Chut_N.

Indeed, an instantaneous regime oscillates too much and an average regime always has a delay. As shown in Figure 1d, the value of the approximate average speed current NCour of the engine can be calculated according to the following equation:

NCour = N der PMH + V_Chut_N. t_dep_der_PMH

N der TDC being the instantaneous speed value at the last Top Dead Center, V_Chut_N the slope of the average speed drop and t_dep_der_PMH the duration since the last Top Dead Center.

This current approximate average speed value can be compared to a speed forming the upper limit NLim of the critical speed zone and an approximation of second duration t_N_Lim reached by the engine speed of the upper limit N Lim of the zone critical can be calculated according to the following equation:

t_N_Lim = (N Cour - N Lim) / V_Chut_N

N Cour being the value of the current approximate average speed, N Lim the engine speed of the upper bound and V_Chut_N the slope of the average speed drop.

The regime forming the upper limit N Lim of the critical regime zone can be a calibratable regime. As a safety measure, a calibrable time delay tempo_N_Lim can be added to this calculation.

In Figures 1d and 1e, Cmd_Pos_lnt denotes the position control of the phase shifter initiating a movement towards the flow angle increased by the intermediate position of said at least one phase shifter and Cmd_Pos_Repos denotes the position control of the phase shifter initiating a movement towards the position angle "minimum air" of the position minimizing the admission of air to the iso-pressure motor of said at least one phase shifter during the stopping of said at least one phase shifter. N Court is the current regime.

The reference tempo_N_Lim designates the time delay related to exceeding the limit speed by modifying a second limit duration t_N_Lim in the second corrected limit duration t_N_Lim corrected. AOA Rep designates the "minimum air" position setpoint of the position minimizing the admission of air to the iso-pressure motor of said at least one phase shifter during stop and AOA Inter the intermediate position setpoint of said at least one phase shifter during shutdown. AOA Court designates the setpoint of the angular position of said at least one phase shifter at a given instant. AOA Ral designates the idle setpoint. V Dephas designates the speed of the phase shifter.

As shown in Figure 1e, the second duration of reaching by the engine speed of the upper limit N Lim of the critical zone can be compared to the first duration of passage. If the first passage time is greater than or equal to the second reaching time, said at least one phase shifter is placed in the position minimizing the admission of air to the motor. This means that the second phase must be started to return the said at least one phase shifter to its position minimizing the intake of air to the motor.

Figures 2 and 3 show three simplified functional modeling curves of the implementation of the method according to the invention with fixed time step. The curve with squares symbolizes the instantaneous engine speed, the curve with circles symbolizes the position reference of the phase shifter and the curve with triangles symbolizes the position of the phase shifter assuming a constant speed of displacement of the phase shifter but with different calibrations according to the direction of rotation as a function of time.

The invention also relates to a motor vehicle comprising a heat engine associated with an automatic engine stop and restart system, the engine having at least one camshaft phase shifter. During an engine stop phase caused by the automatic engine stop and restart system, said at least one phase shifter is controlled in accordance with such a control method.

The invention is in no way limited to the embodiments described and illustrated which have been given only by way of examples.

Claims (10)

Claims: 1. Method for controlling at least one phase shifter of a camshaft of a thermal engine of a motor vehicle during an engine shutdown phase, said at least one phase shifter being, from a position of slowed down at the start of the phase, placed in a position minimizing the admission of air to the iso-pressure motor, characterized in that, during the motor stopping phase, said at least one phase shifter is placed in an intermediate position between the idle position and the position minimizing the intake of air to the engine, with in this intermediate position an increase in an air flow to the engine relative to the position minimizing the intake of air, this intermediate position being maintained as long as an engine speed is above a calculated speed threshold (N_Lim), said at least one phase shifter being placed in the position minimizing the admission of air to the engine as soon as the engine speed is lower than himself engine speed (N_Lim) calculated engine and in which a critical speed zone is defined in which, from an upper bound of this critical speed zone acting as the calculated speed threshold (N_Lim), said at least one phase shifter is placed in the position minimizing the intake of air to the motor, the critical speed threshold (N_Lim) being calculated according to, on the one hand, a first duration of passage of said at least one phase shifter to pass from its current intermediate position at the position minimizing the admission of air to the engine and, on the other hand, a second duration of reaching by the engine speed of the upper terminal (N_Lim) of the critical zone. 2. Method according to claim 1, in which the placement in the intermediate position is done with respect to one or more operating parameters of the engine such as an instant of request to cut off a fuel injection into the engine and / or ignition, an instant of actual cut-off of the injection and / or ignition, these parameters being taken with or without time delay. 3. Method according to claim 2, in which a phase shift setpoint (AOAJnter) is issued aiming to place said at least one phase shifter in the intermediate position, this phase shift setpoint (AOAJnter) being maintained as long as the engine speed is above the calculated engine speed threshold (N_Lim). 4. Method according to any one of claims 1 to 3, in which the first passage time is calculated as a function of the difference in angular position between the intermediate position and the position minimizing the admission of air to the engine divided by the angular speed of said at least one phase shifter. 5. Method according to claim 4, in which the angular speed of said at least one phase shifter is estimated by calibration, with a specific calibration for each direction of rotation of said at least one phase shifter and an identification of the direction of rotation of said at least one phase shifter. at calculation or the angular speed of said at least one phase shifter is estimated and continuously corrected. 6. Method according to any one of the preceding claims, in which, for the calculation of the second duration of reaching by the engine speed of the upper bound (N_Lim) of the critical zone, an instantaneous speed value is noted at a last Top Dead Center of the engine passed since the start of the stop phase, then a time count is triggered from this last Top Dead Center until a new Top Dead Center to replace the last Neutral High, the instantaneous speed value at this last Top Dead Center becoming the instantaneous speed value at the penultimate Top Dead Center, the time count giving a duration between the penultimate Top Dead Center and the last top Dead Center and a slope is calculated mean engine speed drop V_Chut_N according to the equation: V_Chut_N = (N_der_PMH - N_penult_PMH) / t_ent_2_der_PM N_der_PMH being the instantaneous speed value at the last top dead center, N_penult_PMH being the instantaneous speed value at the penultimate top dead center and t_ent_2_der_PM the time between the penultimate top dead center and the last dead center , a value of approximate average speed current of the engine being calculated as a function of the slope of average speed drop (V_Shut_N). 7. Method according to claim 6, in which the value of the approximate average speed current N_Cour of the engine is calculated according to the following equation: N_Cour = N_der_PMH + V_Chut_N. t_dep_der_PMH N_der_PMH being the instantaneous speed value at the last Top Dead Center, V_Chut_N the slope of the average speed drop and t_dep_der_PMH the duration since the last Top Dead Center, this value of current approximate average speed being compared to a speed forming the upper bound (N_Lim ) of the critical speed zone and an approximation of second duration t_N_Lim reached by the engine speed of the upper bound (N_Lim) of the critical zone being calculated according to the following equation: t_N_Lim = (N_Cour - N_Lim) / V_Chut_N N_Cour being the current approximate average speed value, N_Lim the upper bound ¹ and V_Chut_N the average speed fall slope. 8. Method according to claim 7, in which the second duration of reaching by the engine speed of the upper bound (N_Lim) of the critical zone is compared with the 5 first passage time and, if the first passage time is greater than or equal to the second reaching time, said at least one phase shifter is placed in the position minimizing the admission of air to the motor. 9. Motor vehicle comprising an internal combustion engine associated with an automatic engine stop and restart system, the engine having at least one 10 camshaft phase shifter, characterized in that, during an engine stop phase caused by the automatic engine stop and restart system, said at least one phase shifter is controlled in accordance with a control method said at least one phase shifter according to any one of the preceding claims.