FR3129182A1 - METHOD FOR RESTARTING A THERMAL ENGINE IN THE SHUTDOWN PHASE COMPRISING MANAGEMENT OF RESTART MODES - Google Patents

Abstract

The subject of the present invention is a method for restarting the heat engine of a motor vehicle in which the heat engine is able to be restarted according to a first so-called autonomous restart mode when the instantaneous speed is greater than a first threshold (S1) and according to a second mode of restarting by driving a starting means when the instantaneous speed becomes lower than a second threshold (S2), comprising the following successive steps of stopping control (E1) of the engine at a moment, of determining ( E2) of the value of the idle speed setpoint at the instant of the engine stop command and determination (E3) of the first and/or of the second threshold (S1, S2) as a function of said setpoint value of idle speed at said instant of the stop command and of a speed difference. Figure 3

Description

METHOD FOR RESTARTING A THERMAL ENGINE IN THE SHUTDOWN PHASE COMPRISING MANAGEMENT OF RESTART MODES

The field of the invention relates to a method for restarting the internal combustion engine of a motor vehicle, in particular restarts which take place during a drop in engine speed or in a transient stopping phase. This type of reboot is commonly referred to by the English term “Change of Mind”.

The process of restarting a heat engine following the stop command, when it is still rotating due to inertia, is a generally complex operation because it must be ensured that the engine operating conditions guarantee the success of the operation in a sufficiently short time, of the order of about 1.5 seconds with regard to so-called safety criteria (“Safety” according to the English terminology commonly used). This duration is sometimes exceeded due to the fact that it is necessary to wait for the engine speed to drop to a zero value before restarting it. In this particular situation, the restart is interrupted because the time criterion is exceeded, and a restart failure is incorrectly counted.

Still in a “Safety” approach, in the event of successive restart failures, the engine control unit is generally configured to trigger a safety engine shutdown, designated by the English expression “Safe State”. It is also sought to avoid this resulting situation which is then unjustified.

More precisely, the known restarting strategies provide for a first so-called autonomous restarting mode in which the engine can be restarted by fuel injection control, without the aid of a restarting device. This first mode can be operated successfully only when the engine speed is still above a first threshold, close to idle speed around 700-800 rpm. A second mode of restarting by driving a starter is operable successfully when the engine speed crosses a second speed threshold, below values close to 300-400 rpm.

We know the document US9631596B2 describing a method of an engine restart at rotating speed based on the second mode describing a synchronization of the fuel injection with the control of the pre-engagement of the starter pinion. Fuel injection is triggered in relation to a speed threshold Nr1, around 400 rpm, then when the speed drops below the threshold Nr2, the control unit engages the starter solenoid. In addition, the document JP5313819B2 is known describing a method of restarting with the engine running based on the first so-called autonomous mode in which the pressure of the fuel supplied to the injection valve is set higher than during normal operation during a stop phase and automatic restart.

In addition, the applicant has filed document FR2950388A1 describing a strategy for calculating predictive engine speed in order to improve the accuracy of the information. This information comes in addition to the instantaneous engine speed information conventionally calculated at top dead center, therefore with increasingly low precision when the speed tends towards 0 rpm. This method aims to improve the robustness for various engine control functions, such as improving the restart of the internal combustion engine for example to control the stop cylinder, in particular in motor vehicles equipped with a stop system. and automatic restart.

Restart strategies based on predetermined thresholds, in particular the idle speed setpoint for autonomous restart, present robustness problems that can lead to restart failure depending on the engine operating conditions. Indeed, the idle speed setpoint is a variable value, calculated dynamically in real time according to instantaneous parameters. In some cases, this value decreases until it is incompatible with the autonomous restart and then causes the restart to fail if it is incorrectly commanded. This situation is likely to lead to several successive starting attempts and therefore a cut-out of the engine. In addition, in the speed zone between the first threshold and the second threshold, the restart is not operable. Insufficient robustness of the instantaneous speed information and of the restart thresholds, in particular near the first threshold, generates a risk of failure of the autonomous restart.

There is therefore a need to overcome the aforementioned problems. One objective of the invention is to improve the robustness of the automatic stop and restart function. Another objective of the invention is to ensure that the engine control system is in the right conditions to guarantee restarting when the engine is in the drop in speed phase or in the transient stopping phase.

More specifically, the invention relates to a method for restarting the heat engine of a motor vehicle in which the heat engine is able to be restarted according to a first so-called autonomous restart mode when the instantaneous speed is greater than a first threshold and according to a second mode of restarting by driving a restarting means when the instantaneous speed becomes lower than a second threshold. According to the invention, the method comprises the following successive steps:

- the instantaneous engine stop command,

- determination of the value of the idle speed setpoint at the instant of the engine stop command,

- the determination of the first and/or the second threshold as a function of said idle speed setpoint value at said instant of the stop command and of a speed difference.

According to a variant, the first threshold is equal to said idle speed setpoint value increased by a first speed difference.

According to a variant, the second threshold is equal to said idle speed setpoint value reduced by a second speed difference.

According to a variant, the method further includes the triggering of a time delay at the instant of the engine stop command and includes the activation of a first restart authorization during the time delay.

According to a variant, the method further comprises the activation of a second restart authorization as long as the instantaneous engine speed is greater than the first threshold, and the activation of the second restart authorization as long as the instantaneous engine speed is lower than the second threshold.

According to a variant, the method comprises deactivating the second restart authorization as long as the instantaneous engine speed is between the first threshold and the second threshold.

According to a variant, the restart is controlled only when the first or the second restart authorization is activated.

According to a variant, the method further comprises monitoring a security criterion of a restart sequence, said criterion consisting in calculating the duration between the instant of triggering of said restart sequence when the first or second authorization is activated and the end time of said sequence, and to signal a failure when said duration is greater than a predetermined safety duration.

There is also provided a motor vehicle comprising a thermal engine and an automatic stopping and restarting system of the engine and a control unit of said engine and of said system, in which the control unit is configured to implement the method of restart according to any of the preceding embodiments.

The method according to the invention makes it possible to ensure that the engine control system is in the right conditions to guarantee the restarting when the engine is in the drop in speed phase or in the transient stopping phase. The process freezes the parameters conditioning the restart and triggers a timeout, which improves the robustness of the strategy. In addition, the method provides a mechanism for prohibiting the restart when the conditions are not satisfied with regard to the criteria provided.

Other characteristics and advantages of the present invention will appear more clearly on reading the following detailed description comprising embodiments of the invention given by way of non-limiting examples and illustrated by the appended drawings, in which:

schematically represents a functional flowchart of a motor vehicle powertrain comprising an automatic stop and restart system configured to implement the method according to the invention.

represents a graph illustrating the conditions authorizing the automatic restart of the heat engine in accordance with the method according to the invention.

represents a flowchart of an embodiment of the restart method according to the invention.

In , there is schematically presented an embodiment of the powertrain of a motor vehicle designed to implement the restarting method according to the invention. The powertrain comprises a traction chain comprising an internal combustion heat engine 10, an automated transmission 11 of an engine torque to the wheels 12 of the vehicle, an automatic stopping and restarting system 13 of the heat engine 10, in particular. Furthermore, the automated transmission 11 is an automatic or semi-automatic gearbox transmission. It includes a clutch device associated with the gearbox (not shown in ), which are controlled automatically by a control unit for torque transmission and gear changes. The invention applies to any type of traction chain comprising a heat engine and automatic stop and restart system. A person skilled in the art will know how to adapt the invention to the desired architecture.

The thermal engine 10 is controlled by a computer control unit 14, commonly called ECU for “Electronic Control Unit” in English, and comprises means and sensors for determining, in particular, the instantaneous speed of the engine 10, value expressed in revolutions per minute for example. The control unit 14 comprises means for controlling the automatic stop and restart in cooperation with the system 13. An engine stop command consists in controlling the cut-off of the fuel injection, the motor shaft remains in rotation under the effect of the inertia of the mobile coupling for a period. The engine speed drops, possibly down to a zero speed value if it is not restarted before. In a "Change of Mind" situation, the restart sequence consists of driving the motor shaft in rotation, by fuel injection according to a first autonomous mode M1, or by means of a restart device according to a second mode M2. A sequence is delimited by the instant of triggering of the restart command and by the end instant, corresponding to the moment from which the motor is considered to be "autonomous"; i.e. turning by fuel injection alone, at an engine speed equal to or greater than a predetermined engine speed, close to idle speed.

The stopping and restarting sequences are coordinated by the control unit 14 according to status and control signals via the permanent communication of status information to the other systems, such as information indicating whether the engine is running, stopped or in the process of stopping, if a restart is carried out using the starter or in autonomous mode, for example. To this end, the powertrain comprises communication means 15, for example a communication bus of the CAN (Controller Area Network) type, or a LIN (Local Interconnect Network) communication bus.

More specifically, a restart requirement signal is, for example, a signal informing whether the driver or a vehicle system requests the restart of the thermal engine 10, for example according to the detection of a vehicle stop, a request for braking, a demand for torque at the wheels resulting from the driver's wishes, a need for cabin air conditioning, or even a need for electric recharging of a battery. For example, when stationary or in a low-speed braking situation, automatic stop and restart strategies control the stopping of motor 10. For example, the restart requirement signal is a digital signal coding in a first state a restart request or a need with the engine running and, in a second state, encoding the absence of a need with the engine running.

A restart authorization signal is for example a signal controlled by the control unit 14 of the heat engine 10 whose function is to inhibit and authorize the restart command of the heat engine in the event of detection of a need. restart, in particular during an automatic shutdown and restart phase. In the context of the invention, this signal determines the windows of opportunity for restarts with guaranteed success. For example, the authorization signal is a digital signal authorizing in a first state the triggering of a restart sequence and, in a second state, inhibiting the triggering of a restart sequence. Several authorization signals specific to each restart mode can be provided by the control unit.

In the context of the invention, a time delay T is also provided. This is a signal whose function is to authorize restarting in the event of detection of a need for restarting immediately after stopping the reboot. The time delay T makes it possible to delimit a restart authorization period and corresponds to the time required to make the fuel injection cut-off effective following the engine stop command. If a restart request is detected during this time delay T, the strategy guarantees its success because fuel injection is still effective. The time delay T is between 150 milliseconds and 300 milliseconds.

In addition, there is provided a parameter storing the value RR of the idle speed setpoint at the instant of an engine stop command. This parameter is advantageously used by the method to freeze the reference from which the control unit 14 calculates the speed thresholds S1 and S2 conditioning the first mode and the second restart mode M1 and M2 respectively. Freezing stabilizes the value of thresholds S1 and S2 and certifies the conditions for authorizing a restart. The parameter is a value representative of the engine speed, expressed for example in revolutions/minute and is updated in the memory of the control unit 14 each time an engine stop command is detected.

The automatic stop and restart system 13 of the heat engine 10, a system called "STT" for "Stop And Start" in English, comprises a restart member of the heat engine 10. The restart member may comprise a starter, or a starter-alternator. The purpose of the restarting member is to operate and rotate the shaft of the heat engine 10. Conventionally, a starter comprises a solenoid which makes it possible to engage the pinion of the starter on the flywheel and an electric motor direct current which makes it possible to rotate the shaft of the heat engine 10.

The control unit 14 is in charge of the restart strategy during an automatic stop and restart phase in accordance with the method according to the invention. The control unit 14 is capable of controlling the first so-called autonomous restart mode M1 in which the engine 10 can be restarted by fuel injection control, without help from the starter 13. This first mode M1 is operable when the instantaneous speed is still greater than the first threshold S1. The second restart mode M2 by driving the starter 13 is operable when the engine speed drops below the second speed threshold S2.

According to the invention, the first threshold S1 is calculated according to the following relationship: S1=RR+R1, where RR is the value of the idle speed setpoint at the instant of the engine stop command and where R1 is a diet deviation. R1 is between 150 rpm and 350 rpm, preferably R1 is equal to 250 rpm. R1 is a predetermined and calibratable parameter, stored in the memory of the control unit 14. Alternatively, R1 is a function of the outside temperature or of the temperature of the engine cooling water circuit.

The second threshold S2 is calculated according to the following relationship: S2=RR-R2, where RR is the value of the idle speed setpoint at the instant of the engine stop command and where R2 is a speed difference. R2 is between 400 rpm and 600 rpm, preferably R2 is equal to 500 rpm. R2 is a calibratable parameter recorded in the memory of the control unit 14. As a variant, R2 is a function of the outside temperature or of the temperature of the engine cooling water circuit.

It is contemplated that only S1 or only S2 is calculated based on the RR value.

A restart monitoring module is also provided for diagnostic purposes, based on so-called “safety” monitoring criteria. A first criterion consists in calculating the duration between the instant of triggering of a restart sequence and the end instant of said sequence. A second criterion consists in calculating the number of successive restart failures. If the duration and the number of successive failures are exceeded, the control unit 14 signals a failure and controls the engine shutdown.

In , a graph is shown schematically illustrating the instantaneous engine speed during an engine shutdown sequence, in engine speed value Rg on the ordinate, expressed in revolutions per minute, as a function of a time axis t on the abscissa, expressed in seconds. The restart authorization zones Z1, Z2 and Z3 are illustrated in hatched zones. Z1 represents the zone where the restart authorization signal is activated if the instantaneous speed Rg is greater than S1. Z2 represents the zone where the authorization signal is activated if the instantaneous speed Rg is lower than S2. Z3 represents the zone where the authorization signal is activated during the time delay T, between times t1 and t2, whatever the value of the speed Rg. Zone Z4, not hatched, is the zone where the authorization signal inhibits the restart command.

In , the restart control method according to the invention is shown. The control unit 14, with reference to the , is provided with an integrated circuit computer and electronic memories, the computer and the memories being configured to execute said restart method. But this is not mandatory. Indeed, the computer could be external to the control unit 14, while being coupled to the latter 14. In the latter case, it can itself be arranged in the form of a dedicated computer comprising a possible dedicated program , For example. Consequently, the control unit, according to the invention, can be produced in the form of software (or computer (or even “software”)) modules, or else of electronic circuits (or “hardware”), or even of a combination of electronic circuits and software modules.

At a first step E1, the control unit controls a stop E1 of the engine at time t1. From t1, the control unit triggers the fuel injection cut-off and the engine speed begins to drop.

According to the method, the control unit then determines in a step E2 the value RR, corresponding to the value of the idle speed setpoint calculated by the engine control unit at time t1. The RR value is stored by the control unit and is frozen at time t1 to calculate S1 and S2 for this restart sequence specifically. The RR value is used to freeze and stabilize the thresholds S1 and S2. In addition, the control unit triggers timer T at time t1. As can be seen on the , t2 is the end time of the time delay T, corresponding to the delay between the command and the execution of the injection cut-off.

According to the method, the control unit determines in a third step E3 the threshold S1 and the threshold S2. The threshold S1 is calculated according to the value RR increased by the value R1. The threshold S2 is calculated according to the value RR minus the value R2.

In addition, during step E3, the method permanently comprises the monitoring of the instantaneous speed Rg with respect to the thresholds S1 and S2, as well as the activation state of the time delay T. A restart sequence is controlled according to the following strategies during the engine stop phase.

As long as the instantaneous speed Rg is greater than the threshold S1, in the zone Z1 with reference to the , the method includes an activation step E4 of the restart authorization signal. The authorization signal is controlled in the state authorizing the restart. In the event of detection of a need for the motor rotating in the zone Z1, illustrated by the time Dem_t3, the control unit triggers the restart according to the first mode M1 called autonomous restart. Restarting is triggered by a fuel injection command, without using the starter.

When the instantaneous speed becomes lower than S2, in zone Z2 with reference to the , the method includes an activation step E5 of the restart authorization signal. The authorization signal is controlled in the state authorizing the restart. In the event of detection of a need for the motor rotating in the zone Z2, illustrated by the instant Dem_t5, the control unit triggers the restart according to the second mode M2. The restart is triggered by driving the engine shaft by means of the starter until a sufficient speed is reached to control the fuel injection.

As long as the instantaneous speed is between S1 and S2, in zone Z4 with reference to the , the method includes a step E6 of controlling restart inhibition. The authorization signal is driven to the state inhibiting the restart. In the event of detection of a need for the motor rotating in zone Z4, illustrated by instant Dem_t4, the control unit prohibits restarting.

In addition, during the time delay T, between t1 and t2, the method includes a step E7 of activating a restart authorization signal. This corresponds to zone Z3 with reference to the . In the event of detection of a need for the engine running in the zone Z3, independently of the value of the engine speed, the control unit triggers the restart according to the second mode M2 called autonomous mode by fuel injection. This authorization signal remains active during the time delay T even when the engine speed is below the threshold S2. This authorization signal is deactivated once the timer is over.

Furthermore, the method permanently comprises the determination of the safety criteria, in particular the duration of a restart sequence and the number of restart failures. According to the method, the duration criterion of a restart calculates the duration from the instant of effective triggering of the restart when the authorization signal is activated. With reference to the , it would be time Dem_t3 or Dem_t5. Time Dem_t4 would not trigger the calculation of the monitoring duration. This method of calculation makes it possible to avoid reporting a failure that would not be justified. In addition, if a predetermined safety time of about 1.5 seconds is exceeded, the method signals a fault to an engine diagnostic system. Eventually, a motor shutdown is triggered.

Claims (9)

Method for restarting the heat engine of a motor vehicle in which the heat engine is capable of being restarted according to a first so-called autonomous restart mode (M1) when the instantaneous speed (Rg) is greater than a first threshold (S1) and according a second restart mode (M2) by driving a restart means (13) when the instantaneous speed (Rg) becomes lower than a second threshold (S2), characterized in that it comprises the following successive steps:

• the stop command (E1) of the motor at a time (t1),
• the determination (E2) of the value (RR) of the idle speed setpoint at the instant (t1) of the engine stop command,
• the determination (E3) of the first and/or of the second threshold (S1, S2) as a function of said idle speed setpoint value (RR) at said instant (t1) of the stop command and of a speed deviation ( R1; R2).

Method for restarting the heat engine according to claim 1, characterized in that the first threshold (S1) is equal to the said value (RR) of the idle speed setpoint increased by a first speed difference (R1). Method for restarting the heat engine according to Claim 1 or 2, characterized in that the second threshold (S2) is equal to the said value (RR) of the idle speed setpoint reduced by a second difference in speed (R2). Process for restarting the heat engine according to any one of Claims 1 to 3, characterized in that it further comprises the triggering (E2) of a time delay (T) at the instant (t1) of the command to stopping the engine (10) and in that it comprises the activation (E7) of a first restart authorization during the time delay (T). Process for restarting the combustion engine according to any one of Claims 1 to 4, characterized in that it further comprises the activation of a second restart authorization (E4) as long as the instantaneous engine speed (Rg) is higher at the first threshold (S1), and the activation of the second restart authorization (E5) as long as the instantaneous engine speed (Rg) is below the second threshold (S2). Process for restarting the thermal engine according to claim 5, characterized in that it includes the deactivation of the second restart authorization (E6) when the instantaneous engine speed (Rg) is between the first threshold (S1) and the second threshold (S2). Method for restarting the heat engine according to any one of Claims 4 to 6, characterized in that the restart is controlled only when the first or second restart authorization is activated. Method for restarting the thermal engine according to any one of Claims 4 to 7, characterized in that it also comprises monitoring of a safety criterion of a restart sequence, the said criterion consisting in calculating the duration between the instant of triggering of said restart sequence when the first or second authorization is activated and the end instant of said sequence, and to signal a failure when said duration is greater than a predetermined safety duration. Motor vehicle comprising a combustion engine (10) and an automatic stopping and restarting system (13) of the engine (10) and a control unit (14) of said engine (10) and of said system (13), characterized in that the control unit (14) is configured to implement the restart method according to any one of claims 1 to 8.