METHOD FOR RESTARTING AN INTERNAL COMBUSTION ENGINE FROM A STOPPED STATE, INCLUDING RESTART MODE MANAGEMENT

Abstract

The present invention relates to a method for restarting the internal combustion engine of a motor vehicle, in which the internal combustion engine is capable of being restarted according to a first, so-called autonomous restart mode when the instantaneous engine speed is above a first threshold (S1), and according to a second restart mode by driving a starting means when the instantaneous engine speed falls below a second threshold (S2). The method comprises the following successive steps: a shutdown command (E1) of the engine at a given instant; determination (E2) of the idle speed setpoint value at the instant of the engine shutdown command; and determination (E3) of the first and / or second threshold (S1, S2) as a function of said idle speed setpoint value at said instant of the shutdown command and an engine speed deviation. Figure 3

Description

Title of the invention: METHOD FOR RESTARTING AN INTERNAL COMBUSTION ENGINE FROM A STOPPED PHASE INCLUDING RESTART MODE MANAGEMENT

[0001] The field of the invention relates to a method for restarting the internal combustion engine of a motor vehicle, in particular restarts that take place during a drop in engine speed or during a transient phase of stopping. This type of restart is commonly referred to by the English term "Change of Mind".

[0002] The process of restarting an internal combustion engine following a shutdown command, while it is still running due to inertia, is generally a complex operation because it is necessary to ensure that the operating conditions of the internal combustion engine guarantee the success of the operation within a sufficiently short time, on the order of approximately 1.5 seconds, according to so-called safety criteria. This duration is sometimes exceeded because it is necessary to wait for the engine speed to drop to zero before restarting. In this particular situation, the restart is interrupted because the time criterion has been exceeded, and a restart failure is incorrectly recorded.

[0003] Still within a "Safety" approach, in the event of successive restart failures, the engine control unit is generally configured to trigger a safety engine shutdown, referred to by the English expression "Safe State". This resulting situation, which is then unjustified, is also to be avoided.

[0004] More specifically, known restart strategies include a first mode, called autonomous restart, in which the engine can be restarted by fuel injection command, without the assistance of a restarting device. This first mode is successful only when the engine speed is still above a first threshold, close to the idle speed of around 700-800 rpm. A second restart mode, involving starter motor engagement, is successful when the engine speed falls below a second speed threshold, close to values ​​close to 300-400 rpm.

[0005] US patent US9631596B2 is known, describing a method for restarting an engine at running speed based on the second mode describing synchronization of fuel injection with the pre-engagement control of the starter pinion. Fuel injection is triggered relative to a speed threshold Nrl, around 400 rpm, and then when the speed drops below the threshold Nr2, the control unit engages the starter solenoid. Furthermore, the document JP5313819B2 describing a running engine restart method based on the first so-called autonomous mode in which the fuel pressure supplied to the injection valve is set higher than during normal operation during an automatic stop and restart phase.

[0006] Furthermore, the applicant has filed document FR2950388A1 describing a strategy for calculating a predictive engine speed in order to improve the accuracy of the information. This information complements the instantaneous engine speed information conventionally calculated at top dead center, and therefore with increasingly lower accuracy as the engine speed approaches 0 rpm. This method aims to improve the robustness of various engine control functions, such as improving the restart of the internal combustion engine, for example, to control the stop cylinder, particularly in motor vehicles equipped with an automatic stop-start system.

[0007] Restart strategies based on predetermined thresholds, particularly the idle speed setpoint for autonomous restart, present robustness issues that can lead to restart failure depending on 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 autonomous restart, causing restart failure if it is incorrectly initiated. This situation can lead to several successive start attempts and therefore engine shutdown. Furthermore, in the engine speed range between the first and second thresholds, restarting is not possible. Insufficient robustness of the instantaneous engine speed information and the restart thresholds, especially near the first threshold, creates a risk of autonomous restart failure.

[0008] There is therefore a need to address 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 correct condition to guarantee successful restarting when the engine is in a deceleration phase or in a transient stop phase.

[0009] More specifically, the invention relates to a method for restarting the internal combustion engine of a motor vehicle, in which the internal combustion engine is capable of being restarted according to a first, so-called autonomous restart mode when the instantaneous engine speed is above a first threshold, and according to a second restart mode by driving a restarting means when the instantaneous engine speed falls below a second threshold. According to the invention, the method comprises the following successive steps:

[0010] - the engine stop command at a specific time,

[0011] - determining the value of the idle speed setpoint at the time of the engine stop command,

[0012] - the determination of the first and / or second threshold as a function of said value of idle speed setpoint at the time of the stop command and of an idle speed deviation.

[0013] According to one variant, the first threshold is equal to said value of the idle speed setpoint plus a first speed deviation.

[0014] According to one variant, the second threshold is equal to said value of the idle speed setpoint less a second speed deviation.

[0015] According to one variant, the method further includes triggering a time delay at the moment of the motor stop command and includes activating a first restart authorization during the time delay.

[0016] According to one variant, the method further includes the activation of a second restart authorization as long as the instantaneous engine speed is above the first threshold, and the activation of the second restart authorization as long as the instantaneous engine speed is below the second threshold.

[0017] According to one variant, the method involves deactivating the second restart authorization as long as the instantaneous engine speed is between the first threshold and the second threshold.

[0018] According to one variant, the restart is driven only when the first or second restart authorization is enabled.

[0019] According to one variant, the method further includes monitoring a safety criterion of a restart sequence, said criterion consisting of calculating the time between the time of triggering said restart sequence when the first or second authorization is activated and the time of the end of said sequence, and reporting a failure when said time is greater than a predetermined safety time.

[0020] Further, a motor vehicle comprising a thermal engine and an automatic engine stop and restart system and a control unit for said engine and system, in which the control unit is configured to implement the restart process according to any one of the preceding embodiments.

[0021] The method according to the invention makes it possible to ensure that the engine control system is in the correct condition to guarantee a successful restart when the engine is in a speed drop phase or in a transient shutdown phase. The method freezes the parameters conditioning the restart and triggers a time delay, which improves the robustness of the strategy. Furthermore, the method includes a mechanism to prohibit restarting when the conditions are not met with regard to the criteria provided.

[0022] Other features and advantages of the present invention will become more apparent upon reading the following detailed description, which includes embodiments of the invention given by way of non-limiting examples and illustrated by the accompanying drawings, in which:

[0023] [Fig. 1] schematically represents a functional logic diagram of a motor vehicle powertrain comprising an automatic stop and restart system configured to implement the method according to the invention.

[0024] [Fig.2] represents a graph illustrating the conditions allowing the restart automatic operation of the internal combustion engine according to the method according to the invention.

[0025] [Fig.3] represents a flowchart of one embodiment of the process of restart according to the invention.

[0026] Figure 1 schematically illustrates an embodiment of a motor vehicle powertrain designed to implement the restart method according to the invention. The powertrain comprises a drivetrain including an internal combustion engine 10, an automated transmission 11 of engine torque to the wheels 12 of the vehicle, and an automatic stop-start system 13 for the internal combustion engine 10, among other things. Furthermore, the automated transmission 11 is an automatic or semi-automatic gearbox. It includes a clutch device associated with the gearbox (not shown in Figure 1), which is automatically controlled by a control unit for torque transmission and gear changes. The invention is applicable to any type of drivetrain comprising an internal combustion engine and an automatic stop-start system.A skilled professional will be able to adapt the invention to the desired architecture.

[0027] The internal combustion engine 10 is controlled by a computer-based control unit 14, commonly called an ECU for “Electronic Control Unit,” and includes means and sensors for determining, in particular, the instantaneous speed of the engine 10, a value expressed, for example, in revolutions per minute. The control unit 14 includes means for controlling automatic shutdown and restart in cooperation with the system 13. An engine shutdown command consists of controlling the interruption of fuel injection; the engine shaft continues to rotate due to the inertia of the moving coupling for a period. The engine speed drops, possibly to zero if it is not restarted beforehand. In a “Change of Mind” situation, the restart sequence consists of rotating the engine shaft, either 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 moment of triggering the restart command and by the moment of end, corresponding to the moment from which the engine is considered "autonomous"; that is to say - running by fuel injection alone, at a speed value equal to or greater than a predetermined speed, close to the idle speed.

[0028] The stop and restart sequences are coordinated by the control unit 14 based on status and control signals via the continuous communication of status information to other systems, such as information indicating whether the engine is running, stopped, or stopping, whether a restart is being performed using the starter motor or in autonomous mode, for example. For this purpose, the powertrain includes communication means 15, for example a CAN (Controller Area Network) type communication bus, or a LIN (Local Interconnect Network) communication bus.

[0029] More specifically, a restart need signal is, for example, a signal indicating whether the driver or a vehicle system requests the restart of the internal combustion engine 10, for example, based on the detection of a vehicle stop, a braking request, a torque demand at the wheels resulting from the driver's input, a need for cabin air conditioning, or even a need to recharge a battery. For example, when stopped or braking at low speed, automatic stop-start strategies control the shutdown of the engine 10. For example, the restart need signal is a digital signal encoding, in a first state, a restart request or a need for the engine to run, and, in a second state, encoding the absence of a need for the engine to run.

[0030] A restart authorization signal is, for example, a signal controlled by the control unit 14 of the internal combustion engine 10, the function of which is to inhibit and authorize the restart command of the internal combustion engine when a need to restart is detected, particularly during an automatic stop-start phase. Within the scope of the invention, this signal determines the windows of opportunity for a guaranteed successful restart. For example, the authorization signal is a digital signal that, in a first state, authorizes the initiation of a restart sequence and, in a second state, inhibits the initiation of a restart sequence. Several authorization signals specific to each restart mode can be provided by the control unit.

[0031] In the context of the invention, a time delay T is further provided. This is a signal whose function is to authorize restarting if a need to restart is detected immediately after the restart has stopped. The time delay T defines a restart authorization period and corresponds to the time required for the fuel injection to effectively shut off following the engine shutdown command. If a restart request is detected during This time delay T ensures the strategy's success because fuel injection is still active. The time delay T is between 150 milliseconds and 300 milliseconds.

[0032] Furthermore, a parameter is provided for storing the RR value of the idle speed setpoint at the moment an engine stop command is issued. This parameter is advantageously used by the method to fix the reference from which the control unit 14 calculates the engine speed thresholds SI and S2 that condition the first and second restart modes M1 and M2, respectively. This fixing stabilizes the values ​​of the thresholds SI and S2 and confirms the conditions for authorizing a restart. The parameter is a value representing the engine speed, expressed, for example, in revolutions per minute, and is updated in the memory of the control unit 14 each time an engine stop command is detected.

[0033] The automatic stop-start system 13 of the internal combustion engine 10, known as the "STT" system for "Stop and Start," includes a restarting device for the internal combustion engine 10. The restarting device may include a starter motor or an alternator-starter. The purpose of the restarting device is to start and rotate the shaft of the internal combustion engine 10. Typically, a starter motor includes a solenoid that engages the starter pinion with the flywheel and a DC electric motor that rotates the shaft of the internal combustion engine 10.

[0034] The control unit 14 is responsible for the restart strategy during an automatic stop-start phase according to the method of the invention. The control unit 14 is capable of controlling the first mode M1, known as autonomous restart, in which the engine 10 can be restarted by fuel injection command, without assistance from the starter 13. This first mode M1 is operable when the instantaneous engine speed is still above the first threshold SL. The second restart mode M2, by driving the starter 13, is operable when the engine speed falls below the second engine speed threshold S2.

[0035] According to the invention, the first threshold SI is calculated according to the following relationship: S1 = RR + R1, where RR is the idle speed setpoint value at the time the engine stop command is given and where RI is a speed deviation. RI is between 150 rpm and 350 rpm, preferably RI is equal to 250 rpm. RI is a predetermined and calibratable parameter, stored in the memory of the control unit 14. Alternatively, RI is a function of the outside temperature or the temperature of the engine cooling water circuit.

[0036] The second threshold S2 is calculated according to the following relationship: S2 = RR - R2, where RR is the idle speed setpoint value at the moment the engine stop command is given and where R2 is a speed deviation. R2 is between 400 rpm and 600 rpm. The preferred R2 is equal to 500 rpm. R2 is a calibrable parameter stored in the memory of the control unit 14. Alternatively, R2 is a function of the outside temperature or the temperature of the engine cooling water circuit.

[0037] It is envisaged that only SI or only S2 will be calculated as a function of the RR value.

[0038] A restart monitoring module is also provided for the purpose of Diagnostics are based on so-called "safety" monitoring criteria. The first criterion calculates the time between the start of a restart sequence and its completion. The second criterion calculates the number of consecutive restart failures. If the duration and number of consecutive failures are exceeded, the control unit 14 signals a fault and shuts down the engine.

[0039] In [Fig. 2], a schematic graph is shown illustrating the instantaneous engine speed during an engine shutdown sequence, with the 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 shown in hatched areas. Z1 represents the zone where the restart authorization signal is activated if the instantaneous engine speed Rg is greater than SL. Z2 represents the zone where the authorization signal is activated if the instantaneous engine speed Rg is less than S2. Z3 represents the zone where the authorization signal is activated during the time interval T, between times t1 and t2, regardless of the engine speed value Rg. The unhatched zone Z4 is the zone where the authorization signal inhibits the restart command.

[0040] Figure 3 illustrates the restart control method according to the invention. The control unit 14, referred to in Figure 1, is equipped with an integrated circuit computer and electronic memories, the computer and memories being configured to execute said restart method. However, this is not mandatory. Indeed, the computer could be external to the control unit 14, while still being coupled to it. In this latter case, it could itself be arranged as a dedicated computer including, for example, a dedicated program. Consequently, the control unit, according to the invention, can be implemented in the form of software modules, electronic circuits, or hardware, or a combination of electronic circuits and software modules.

[0041] In a first step El, the control unit controls an engine shutdown El at time tl. From tl, the control unit triggers the fuel injection cut-off and the engine speed begins to fall.

[0042] According to the method, the control unit then determines at a step E2 the value RR, corresponding to the value of the idle speed setpoint calculated by the unit The engine control unit stores the RR value at time tl and sets it to a fixed value at time tl to calculate SI and S2 for this specific restart sequence. The RR value allows the thresholds S1 and S2 to be fixed and stabilized. Furthermore, the control unit triggers the time delay T at time tl. As shown in [Fig. 2], t2 is the end time of the time delay T, corresponding to the delay between the command and the actual injection cut-off.

[0043] According to the method, the control unit determines the SI threshold and the S2 threshold in a third step E3. The SI threshold is calculated based on the RR value increased by the RL value. The S2 threshold is calculated based on the RR value decreased by the R2 value.

[0044] In addition, during step E3, the process continuously monitors the instantaneous speed Rg with respect to the thresholds SI and S2, as well as the activation state of the timer T. A restart sequence is controlled according to the following strategies during the engine shutdown phase.

[0045] As long as the instantaneous operating speed Rg is above the threshold SI, in zone ZI as shown in [Fig. 2], the method includes an activation step E4 of the restart authorization signal. The authorization signal is driven to the state allowing the restart. If a need for the running engine is detected in zone Zl, illustrated by the instant Dem_t3, the control unit triggers the restart according to the first mode Ml, known as autonomous restart. The restart is triggered by a fuel injection command, without using the starter.

[0046] When the instantaneous engine speed falls below S2, in zone Z2 as shown in [Fig. 2], the method includes an activation step E5 of the restart authorization signal. The authorization signal is driven to the state allowing the restart. If a need for the running engine is detected in zone Z2, illustrated by the instant Dem_t5, the control unit triggers the restart according to the second mode M2. The restart is initiated by driving the engine shaft using the starter until a sufficient speed is reached to control fuel injection.

[0047] As long as the instantaneous operating conditions are between SI and S2, in zone Z4 as shown in [Fig. 2], the method includes a control step E6 that inhibits restarting. The enabling signal is driven in the state that inhibits restarting. If a need for the motor to run is detected in zone Z4, as illustrated by the instant Dem_t4, the control unit prevents restarting.

[0048] Furthermore, during the time interval T, between t1 and t2, the method includes an activation step E7 of a restart authorization signal. This corresponds to zone Z3 with reference to [Fig. 2]. If a need for the motor to run is detected in zone Z3, regardless of the motor speed, the control unit triggers the restart according to the second mode M2, called autonomous mode. 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 time delay has ended.

[0049] Furthermore, the method continuously determines safety criteria, including the duration of a restart sequence and the number of failed restarts. According to the method, the restart duration criterion calculates the duration from the actual restart trigger moment when the authorization signal is activated. Referring to [Fig. 2], this would be time Dem_t3 or Dem_t5. Time Dem_t4 would not trigger the calculation of the monitoring duration. This calculation method avoids reporting an unjustified fault. In addition, if a predetermined safety duration of approximately 1.5 seconds is exceeded, the method signals a fault to an engine diagnostic system. Optionally, an engine shutdown is triggered.

Claims

Demands

1. A method for restarting the internal combustion engine of a motor vehicle in which the internal combustion engine is capable of being restarted according to a first restart mode (M1) called autonomous when the instantaneous speed (Rg) is greater than a first threshold (SI) and according to a second restart mode (M2) by driving a restarting means (13) when the instantaneous speed (Rg) becomes less than a second threshold (S2), characterized in that it comprises the following successive steps: - the engine stop command (E1) at a time (t1), - the determination (E2) of the value (RR) of the idle speed setpoint at the time (t1) of the engine stop command, - the determination (E3) of the first and / or second threshold (SI, S2) as a function of said value (RR) of the idle speed setpoint at said time (t1) of the stop command and of a speed deviation (RI;R2), the first threshold (SI) being equal to said value (RR) of the idle speed setpoint increased by a first speed deviation (RI).;

2. Method for restarting the internal combustion engine according to claim 1, characterized in that the second threshold (S2) is equal to said value (RR) of the idle speed setpoint less a second speed deviation (R2).

3. Method for restarting the heat engine of claim 1 or 2, characterized in that it further comprises the triggering (E2) of a time delay (T) at the instant (tl) of the engine stop command (10) and in that it comprises the activation (E7) of a first authorization of the restart during the time delay (T).

4. Method for restarting the internal combustion engine according to any one of claims 1 to 3, characterized in that it further comprises the activation of a second restart authorization (E4) as long as the instantaneous engine speed (Rg) is above the first threshold (SI), and the activation of the second restart authorization (E5) as long as the instantaneous engine speed (Rg) is below the second threshold (S2).

5. A method for restarting the internal combustion engine according to claim 4, characterized in that it comprises deactivating the second Restart authorization (E6) when the instantaneous engine speed (Rg) is between the first threshold (SI) and the second threshold (S2).

6. Method for restarting the internal combustion engine according to any one of claims 3 to 5, characterized in that the restart is controlled only when the first or second restart authorization is activated.

7. A method for restarting the internal combustion engine according to any one of claims 3 to 6, characterized in that it further comprises monitoring a safety criterion of a restart sequence, said criterion consisting of calculating the time between the moment of triggering said restart sequence when the first or second authorization is activated and the moment of ending said sequence, and signaling a failure when said time is greater than a predetermined safety time.

8. Motor vehicle comprising a heat engine (10) and an automatic engine stop and restart system (13) for the engine (10) and a control unit (14) for said engine (10) and 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 7.

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