WO2011101564A1

WO2011101564A1 - Method and device for controlling restart of a heat engine

Info

Publication number: WO2011101564A1
Application number: PCT/FR2011/050083
Authority: WO
Inventors: Frédéric DUPE
Original assignee: Peugeot Citroën Automobiles SA
Priority date: 2010-02-17
Filing date: 2011-01-18
Publication date: 2011-08-25
Also published as: FR2956447A1; FR2956447B1

Abstract

The invention relates to a method for controlling the restart of an internal combustion heat engine, said method comprising: the assisted heat engine start control (56), wherein an electric motor rotates the shaft of the heat engine, and alternately, the self-contained heat engine start control (54), wherein only the residual rotation of the engine shaft, kept rotating by means of the inertia thereof from the last engine start, is used. Said method is characterized in that it comprises: predicting (40) the engine speed at the next top dead center and selecting between the assisted or self-contained start control according to said predicted speed.

Description

METHOD AND DEVICE FOR CONTROLLING A RESTART OF A

THERMAL MOTOR

The present invention claims the priority of the French application 1051 138 filed February 17, 2010 whose content (text, drawings and claims) is here incorporated by reference.

[Ooo2] The invention relates to a method and a device for controlling a restart of an internal combustion engine, that is to say a start other than a cold start, the example a restart following an automatic shutdown of the engine (hybrid vehicles or equipped with an automatic stop and start system of the Stop & Start engine).

[ooo3] Known methods include:

The control of an assisted start of the heat engine in which an electric motor rotates the shaft of the heat engine, and alternately

The control of an independent start of the engine in which only the residual rotation of the motor shaft maintained in rotation by its inertia since the last stopping of the engine is used.

[ooo4] The autonomous start is a start without recourse to an electric motor of the type starter or alternator-starter to drive the shaft of the thermal engine in rotation. It is made possible by the fact that the motor shaft continues to rotate for a few moments (for example a few hundred milliseconds) after stopping the engine because of its inertia.

[ooo5] The applicant is aware of processes where the choice between assisted or autonomous start is made according to the current engine speed. The engine speed is the number of revolutions per minute of the engine shaft.

[ooo6] Then, the engine speed is compared to a threshold to allow or not the autonomous start of the engine. Since the response time of the engine is not instantaneous, this threshold is oversized. This leads to performing assisted starts in situations where an autonomous start would have been possible. This accelerates the wear of the electric motor used to drive the shaft of the engine.

[Ooo7] The invention aims to remedy this drawback by proposing a method for controlling the restart of a heat engine comprising:

· The prediction of the engine speed to the next top dead center, and

• the choice between the command of assisted or autonomous start according to this predicted mode.

[ooo8] Choosing between assisted and autonomous starts based on the engine speed predicted at the next top dead center can identify more situations in which a standalone start can be achieved. Thus, we reduce the number of assisted starts and therefore the wear of the electric motor used during these assisted starts. As a reminder, the top dead center corresponds to the position of the piston in a cylinder where the volume of the combustion chamber in this cylinder is the smallest.

[ooo9] Embodiments of this method may include one or more of the following features:

The choice is made by comparing the predicted engine speed with a predetermined threshold;

The predetermined threshold is a function of the temperature of the heat engine;

The predicted engine speed is obtained using the following relation:

• N, and Ni ₊ i are, respectively, the current engine speed and the predicted engine speed,

· Ci is the current torque of the motor shaft,

J is the inertia of the shaft of the heat engine, and

• TPMH is the duration between two successive high dead spots;

The duration T _PM H is calculated using the following relation:

where N _C yi is the number of cylinders of the engine.

[Ooio] The invention also relates to an information recording medium comprising instructions for the implementation of the above control method, when these instructions are executed by an electronic computer.

[Ooi i] The invention also relates to a device for controlling the starting of an internal combustion engine, this device comprising a control unit able to:

"Controlling an assisted start of the engine in which an electric motor rotates the shaft of the engine, and alternately,

Controlling an independent start of the engine in which only the residual rotation of the motor shaft maintained in rotation by its inertia since the last stopping of the engine is used,

Predicting the engine speed at the next top dead center, and

• to choose between assisted or autonomous start control according to this predicted mode. Finally, the invention also relates to a vehicle comprising the control device above.

The invention will be better understood on reading the following description given solely by way of non-limiting example and with reference to the drawings in which:

FIG. 1 is a schematic illustration of the architecture of a vehicle equipped with a device for controlling the starting of a heat engine, and

FIG. 2 is a flowchart of a method for controlling the starting of the heat engine of the vehicle of FIG. 1.

In the following description, the features and functions well known to those skilled in the art are not described in detail.

[Ooi 5] Figure 1 partially shows a top view of the front portion of a vehicle 2. For example, the vehicle 2 is a motor vehicle such as a car.

This vehicle 2 is equipped with a combustion engine 4 with internal combustion. This engine 4 is equipped with a shaft 6 which rotates the driving wheels 8, 1 0 of the vehicle.

2.

Typically, the engine 4 is a four-stroke engine equipped with four cylinders 1 2 to 1 5. In such a motor, the shaft 6 makes two turns to achieve a complete cycle of a piston inside the cylinder. The shaft 6 has an inertia noted J and considered constant. Under the effect of this inertia, the shaft 6 can continue to rotate for more than a hundred milliseconds after stopping the engine 4.

The shaft 6 is mechanically connected to a shaft 1 8 of an electric motor 20 via a drive belt 22. The motor 20 is designed to rotate the shaft 6 to allow 4. Typically, the motor 20 is a starter or an alternator-starter. When the motor 20 is used to start the engine 4, it is called assisted starting.

The vehicle 2 also comprises a device 26 for controlling the starting of the engine 4. This device 26 is equipped with a control unit 28 for starting the engine 4. For example, this unit 28 is made from a or a plurality of programmable electronic calculators adapted to execute instructions recorded on an information recording medium. For this purpose, the unit 28 is connected to a memory 30 containing the instructions necessary to execute, inter alia, the method of FIG.

In particular, the memory 30 comprises a mapping PM and mapping SM. The mapping PM associates with each regime N, the engine 4 a torque Ci of loss. This loss torque corresponds to the torque exerted on the shaft 6 by all the forces which slow down the rotation of this shaft. Typically, it is essentially friction forces and resistive couples exerted by different accessories driven in rotation by the shaft 6. For example, the accessory is an alternator, a motor of an air conditioning or other.

This mapping PM is for example built experimentally. For this purpose, for different speeds N, of the engine, the torque C, of this engine is measured.

The map SM associates the value of a threshold Si at different operating conditions of the engine 4. This threshold Si corresponds to a threshold engine speed beyond which an autonomous start of the engine 4 is possible. Here, for simplicity, the threshold Si is only a function of the temperature of the engine 4. Thus, the mapping associates a value of the threshold Si at each engine temperature 4.

For example, the mapping SM is experimentally constructed for different temperatures of the engine 4.

The unit 28 controls the start of the engine 4 according to the procedure known as "stop and start". This control of the engine 4 is to automatically stop the engine 4 when the vehicle is stopped and automatically control the start of the engine 4 when the driver wants to advance. The automatic stopping and starting conditions of the engine are determined from different physical quantities measured on the vehicle 2 such as its speed, the depression of the accelerator pedal, the engagement of a speed or the like.

The unit 28 is able to control an autonomous start of the engine 4 as an assisted start of the engine 4. To choose between these two starting modes, it implements the method of Figure 2. To put the process of FIG. 2, the unit 28 is connected to a sensor 32 of the current engine speed Ni at each top dead center and to a sensor 34 of the engine temperature 4. For example, the sensor 34 measures the temperature engine cooling water 4.

The operation of the device 26 will now be described in more detail with regard to the method of FIG. 2.

After controlling the stopping of the engine 4, the unit 28 proceeds to a step 40 of predicting the engine speed to the next top dead center. This engine regime predicts

For this purpose, during an operation 42, the current engine speed N, at the previous top dead center is measured by the sensor 32.

Then, during an operation 44, the current torque C, the motor 4 is calculated. When the engine is stopped and the shaft 6 continues to turn on its momentum, the current torque Ci is equal to the couple of losses. This torque C is thus calculated using the mapping PM and the value of the torque N, measured during the previous operation.

In the following of this process, it is considered that this pair C is constant between the previous top dead center and the next top dead center reached by one of the Engine pistons 4. With this assumption, during an operation 45, the duration T _PM H between two successive high dead spots is calculated. For this, we know the angular distance R traveled by the shaft 6 between two successive dead spots. This distance R is given by the following relation:

N _cyl where:

• N _C yi is the number of cylinders of the engine 4, that is to say here four, and

• "2" is set by the number of revolutions of the shaft 4 to complete a cycle.

Then, the following dynamic equation is integrated twice to obtain a second degree equation: π_dN_

'30 ^' dt

The term ττ / 30 is introduced because the dynamic equation is expressed with the engine speed N and not with an angular velocity in rad / s.

The equation of the second degree obtained is as follows:

2 days ^PMH 30 ^PMH N _cyl

where TPMH is the duration between two successive high dead spots

By solving this equation of the second degree, the duration TPMH is obtained. The duration T is given by the following relation:

From this duration T _PM H, during an operation 46, the engine speed predicted N _{i +} is calculated using the following relationship: N = N ^X - _T · - · T ^Α ΡΜΗ

J 71

By simplifying the relation above, we obtain the following relation giving the value of the regime N _{i +} i: In parallel with step 40, during a step 50, the unit 28 also calculates the value of the threshold Si using the mapping SM. In step 50, the temperature of the engine 4 is measured by the sensor 34. From this measured temperature and the map SM, the value of the threshold Si is obtained.

In a step 52, the predicted engine speed N _{i +} i is compared with the value of the threshold Si. If the predicted regime exceeds the value of the threshold Si, then, in a step 54, the control of the automatic start of the engine 4. More precisely, during step 54, it is ordered to inject fuel and oxidizer into the cylinders of the engine 4 and then to explode this mixture of fuel and oxidant at the moment when the piston reaches the top dead center. In step 54 the shaft 6 is not rotated by an electric motor.

In the contrary case, that is to say if the engine speed predicts N _{i +} i is lower than the threshold Si then, during a step 56, the unit 28 controls the assisted start of the engine 4. For this, the unit 28 controls the motor 20 to rotate the shaft 6 then the unit 28 controls the injection of fuel and oxidant into the cylinders and their explosion when the top dead center is reached to rotate the shaft 6. When the engine speed reached is greater than a threshold S ₂ , the electric motor 20 is stopped and only the engine 4 is used to drive the shaft 6 in rotation.

At the end of steps 54 or 56, the process returns to steps 40 and 50 which will be performed again during a next start of the engine 4.

Many other embodiments are possible. For example, the threshold Si can be calculated otherwise.

Other engines that a four-stroke four-cylinder engine can be controlled by the device 26. For example, the number of cylinders can be different or the number of revolutions per cycle can be different. In these cases, the different relations given in the particular case of a four-stroke four-cylinder engine are adapted to this new configuration of the engine 4.

The torque C can be measured rather than estimated from the measured engine speed.

Claims

A method for controlling the restart of an internal combustion engine, said method comprising:

The control (56) of an assisted starting of the heat engine in which an electric motor rotates the shaft of the heat engine, and alternately

The control (54) of an autonomous start of the engine in which only the residual rotation of the motor shaft maintained in rotation by its inertia since the last stopping of the engine is used,

characterized in that the method comprises:

• the prediction (40) of the engine speed to the next top dead center, and

The method of claim 1, wherein the selection is made by comparing (52) the predicted engine speed to a predetermined threshold.

3. The method of claim 2, wherein the predetermined threshold is a function of the temperature of the engine.

A method according to any one of the preceding claims, wherein the predicted engine speed is obtained using the following relationship:

J π

Ni and N _{i +} i are, respectively, the current engine speed and the predicted engine speed,

Ci is the current torque of the motor shaft,

J is the inertia of the heat engine shaft, and

TPMH is the duration between two successive high dead spots.

The method of claim 4, wherein the duration T _PM H is calculated using the following relationship:

where N _C yi is the number of cylinders of the engine.

6. Support (30) for recording information, characterized in that it comprises instructions for the execution of a control method according to any one of the preceding claims, when these instructions are executed by a calculator electronic.

7. Device for controlling the restart of an internal combustion engine, this device comprising a control unit (28) capable of:

characterized in that the control unit is also capable of:

Predicting the engine speed at the next top dead center, and

• to choose between assisted or autonomous start control according to this predicted mode.

8. Vehicle (2), characterized in that it comprises a device (26) for controlling the starting of a heat engine according to claim 7.