FR3102810A1 - METHOD OF CONTROL OF A STARTING OF A THERMAL ENGINE IN A HYBRID TRACTION ARCHITECTURE - Google Patents

Abstract

The invention relates to a method of controlling a start-up of a heat engine (11) belonging to a hybrid drive train installed on a train of a motor vehicle provided with wheels, said drive train also comprising an electric motor. traction (13) and a reversible electric machine coupled with the heat engine (11), said method comprising: - a step of determining a number of top dead centers before a first combustion as a function of a wheel torque, and - a step for controlling the start of the heat engine (11) so that the first combustion of the heat engine (11) is controlled after the number of top dead centers previously determined. Figure 2

Description

METHOD FOR CONTROLLING STARTING A THERMAL ENGINE IN A HYBRID TRACTION ARCHITECTURE

The present invention relates to a method for controlling a start of a heat engine in a hybrid traction architecture, in particular for a motor vehicle.

In a manner known per se, a motor vehicle traction chain can comprise a heat engine and an electric traction motor installed on an axle of a motor vehicle, in particular a front axle.

The electric traction motor is coupled to the heat engine via a first clutch. The electric traction motor is coupled with a gearbox via a second clutch. The output shaft of the gearbox is in mesh with the wheels of the vehicle.

In addition, a reversible-type rotating electrical machine is coupled to the heat engine via the accessories front panel, for example also incorporating an air conditioning compressor. To this end, a device for transmitting movement between the heat engine and the electric machine may for example comprise a chain or a belt cooperating with pulleys carried respectively by the crankshaft and the shaft of the machine.

This electric machine, commonly called an alternator-starter, is capable of operating in a generator mode to recharge a battery of the vehicle as well as in a motor mode to ensure starting of the heat engine while the vehicle is stationary or during a transition from an electric driving mode to a thermal driving mode. This electric machine can also be used to supply energy to the battery during a regenerative braking phase.

When the electric motor provides traction for the vehicle, the chocks of the powertrain are under stress because torque is exerted by the wheels. When restarting the combustion engine, in order to have correct longitudinal dynamics and a good level of comfort making the electrical/thermal transition imperceptible, the torque delivered by the combustion engine to the wheels must reach approximately 500- 650ms maximum after driver input.

However, this criterion is not sufficient because the vibration level must also be contained in the longitudinal direction of the vehicle. However, the fact of not being able to control the angular acceleration of the crankshaft in the existing processes does not make it possible to reach an acceptable vibration level.

The invention aims to remedy this drawback effectively by proposing a method for controlling the starting of a heat engine belonging to a hybrid traction chain installed on a train of a motor vehicle provided with wheels, said traction chain comprising also an electric traction motor and a reversible electric machine coupled with the heat engine, the motor vehicle being in an electric driving phase ensured by the electric traction motor and starting of the heat engine being requested, said method comprising:
- a step of determining a number of top dead centers before a first combustion as a function of a wheel torque, and
- a step of controlling the start of the heat engine so that the first combustion of the heat engine is controlled after the number of top dead centers previously determined.

The invention thus makes it possible, by determining the number of top dead centers before the first combustion, to control the angular acceleration of the crankshaft and therefore to reduce the vibration level in the longitudinal direction of the vehicle when the heat engine is restarted, and this without penalizing the longitudinal dynamics of the vehicle. The invention also makes it possible to considerably reduce the dimensioning of the reversible electric machine (the alternator-starter), in terms of mechanical power, since it is possible to delay the first combustion.

According to one implementation, said method comprises a step of determining a power to be supplied to the heat engine for its start-up as a function of the wheel torque, and
- A step of controlling the reversible electric machine so that said reversible electric machine supplies the heat engine with the power necessary for starting.

According to one implementation, the number of top dead centers and the power to be supplied to the thermal engine for its starting as a function of the wheel torque are determined by also taking into account a starting threshold of the thermal engine.

According to one implementation, the number of top dead centers before a first combustion is determined by means of a map.

According to one implementation, the power to be supplied to the thermal engine for its starting is determined by means of a map.

According to one implementation, the starting of the heat engine is controlled over a period of between 500 and 650 ms.

According to one implementation, the electric traction motor and the reversible electric machine are powered by the same battery.

According to one implementation, in the case where the battery is fully charged, a starting threshold of the heat engine is between 7 kW and 9 kW.

According to one implementation, the electric traction motor and the reversible electric machine have an operating voltage of 48 volts.

The invention also relates to a computer comprising a memory storing software instructions for the implementation of the method for controlling a start of a heat engine as defined above.

The invention will be better understood on reading the following description and on examining the accompanying figures. These figures are given only by way of illustration but in no way limit the invention.

FIG. 1 is a schematic representation of a traction chain for a motor vehicle implementing a method for controlling the starting of a heat engine according to the invention;

Figure 2 is a schematic representation illustrating a distribution of electrical and mechanical power between the various components of the traction chain of Figure 1;

Figure 3 is a schematic representation illustrating a kinematics of a powertrain;

Figure 4 is a graphical representation illustrating a feature of a heat engine wedge;

Figure 5 is a graphical representation illustrating a speed and acceleration characteristic of a heat engine crankshaft during start-up;

Figure 6 is a graphical representation illustrating a hybrid strategy based on a state of charge of a traction battery;

FIG. 7 is a graphic representation illustrating the evolution of the pseudo-frequency of the crankshaft during the first revolution with combustion as a function of the speed of the motor vehicle;

Figure 8 is a graphical representation illustrating the evolution of the time required for a heat engine to go from 0 to 2000 revolutions / min as a function of the pseudo-frequency of the crankshaft during the first revolution with combustion respectively for a two-point curve top dead and three top dead centers;

FIG. 9 is a graphic representation illustrating a change in the mechanical power that the alternator-starter must deliver to ensure starting of the heat engine as a function of the pseudo-frequency of the crankshaft during the first revolution with combustion;

FIG. 10 is a graphic representation illustrating the curve of top dead centers to be selected as a function of a power of the alternator-starter required;

FIG. 11 is a schematic representation of a control-command device enabling the implementation of the method according to the invention for controlling the start-up of a heat engine;

FIG. 12 is a diagram of the steps of the method according to the invention for controlling the starting of a heat engine.

FIG. 1 shows a traction chain 10 for a motor vehicle comprising a heat engine 11 associated with a flywheel system 12 and an electric traction motor 13 installed on an axle of a motor vehicle, in particular a front axle. The heat engine 11 is for example a three-cylinder heat engine. Alternatively, the heat engine 11 may of course include a different number of cylinders.

The electric traction motor 13 is coupled to the heat engine 11 via a first clutch K0. The electric traction motor 13 is coupled with a transmission device 15 via a second clutch K1. The transmission device 15 comprises in particular a gearbox and a differential.

The output shaft 16 of the transmission device 15 is in mesh with the wheels of the vehicle 17. In an electric mode of operation, the clutch K0 is open while the clutch K1 is closed. In a thermal operating mode, the two clutches K0 and K1 are closed.

Furthermore, a rotating electric machine 19 of the reversible type is coupled to the heat engine 11 via the accessories front panel also integrating, for example, an air conditioning compressor 20. For this purpose, a motion transmission device 21 between the heat engine 11 and the machine 19 may for example comprise a chain or a belt cooperating with pulleys carried respectively by the crankshaft and the shaft of the electric machine 19.

This electric machine 19, commonly called alternator-starter, is capable of operating in a generator mode to recharge a battery of the vehicle as well as in a motor mode to ensure a start of the heat engine 11 while the vehicle is stationary or during a transition from an electric driving mode to a thermal driving mode. This electric machine 19 can also be used to supply energy to the battery during a regenerative braking phase.

Optionally, it is possible to provide a starter 22 to ensure a cold start of the heat engine 11. In other words, the starter 22 ensures the first start of the heat engine 11. To this end, the starter 22 comprises a pinion of drive meshing with a crown of the heat engine 11.

FIG. 2 illustrates an example of the distribution of electrical power (solid arrow) and mechanical power (dotted arrow) between the various components of the traction chain 10. In the example represented, the alternator-starter 19 and the motor electric traction 13 are powered by the same traction battery 25. The alternator-starter 19 and the electric traction motor 13 may have a supply voltage of 48 volts. A 12 Volt electrical network, referenced 26, is connected to the 48 Volt electrical network via a DC/DC converter 27.

As shown in Figure 3, the heat engine 11 is schematically mounted on a pivot 28. A wedge 29 of motor 11 allows to take up the longitudinal forces along the arrow F1. It should be noted that the greater the force applied to the wedge 29, the less it compresses. The stiffness of the wedge 29 therefore increases.

When restarting the heat engine 11, it is considered that the force on the wheel 17 is constant due to the electric running. The powertrain submits in the longitudinal direction to the body the force to advance plus the alternating forces linked to the restarting of the engine 11. The alternating forces are due to the dynamic balancing of rotation which is not perfect on a heat engine 11 , in particular for a three-cylinder in-line engine. So there are imbalances. In fact, the wedge 29 of the powertrain acts as a damped spring and lets through more or less attenuated vibrations depending on the frequency of the excitation. So that the vibrations are not felt by the driver, it is ensured that the excitation frequency is always higher than the roll frequency of the powertrain, more particularly always above the cut-off pulse "w0" (cf. 4 showing the characteristic of the wedge 29 corresponding to the Mod_amp amplification module as a function of the pulse w). Curve C1 corresponds to low damping and curve C2 corresponds to high damping.

FIG. 5 shows the speed characteristic W_vil of the crankshaft of the internal combustion engine 11 as a function of time during start-up as well as the corresponding acceleration A_vil of the crankshaft.

Knowing the force at the wheel 17 during electric driving as well as the stiffness of the wedge 29 of the thermal engine 11, and by applying a coefficient of 1.5 (in order to have a system at least partially in phase opposition – a coefficient of 2 allows a total phase opposition), then one can deduce the minimum angular acceleration during the restart of the heat engine 11 and at the first combustion. The frequency f0 corresponds to a pseudo-frequency of rotation of the crankshaft during the first revolution with combustion.

As can be seen in FIG. 6, the hybrid strategy is based on the state of charge E_char of the traction battery 25. The heat engine 11 is constantly in operation over the load range P1 comprised between 0 W.h and 60 W.h corresponding to a safe range.

The thermal engine 11 can be momentarily cut off depending on the traffic conditions in an operation of the STT type for "Stop and Start" in English on the load range P2 comprised between 60 and 180 W.h.

The vehicle will be able to operate in pure electric mode on the P3 load range of between 180 and 432 W.h.

In the case where the battery 25 is fully charged, it is possible to have a starting threshold S_mth of the heat engine 11 of the order of 7-9 kW.

By taking into consideration the stiffnesses of the wedge 29 of the powertrain and the starting threshold S_mth of the heat engine 11, then it is possible to calculate a minimum level of the frequency "f0" to be reached as a function of the torque at the wheel 17 which itself depends on the speed of the vehicle V (cf. figure 7).

It is possible by knowing the frequency f0 to be able to choose the number of top dead centers (TDC) before the first combustion of the heat engine 11, as well as the mechanical power that the alternator-starter 19 will have to deliver for starting the heat engine 11 .

FIG. 8 shows the evolution of the duration d (in ms) necessary for a heat engine 11 to go from 0 to 2000 revolutions/min as a function of the frequency f0. Curve C3 was obtained for two top dead points before the first combustion. Curve C4 was obtained for three top dead points before the first combustion. Band B corresponds to an acceptable starting time in terms of pleasure of between 500 and 650 ms.

FIG. 9 shows the evolution of the mechanical power P_mec that the alternator-starter 19 must deliver to ensure starting of the heat engine 11 as a function of the frequency f0. Curve C5 was obtained for two top dead points before the first combustion. Curve C6 was obtained for three top dead points before the first combustion.

For example, as shown in Figure 10, for a target frequency f0 greater than 19 Hz, three top dead points before the first burn can be selected to be in band B. For a target frequency f0 less than 19 Hz, two top dead points can be selected before the first combustion so as to be in band B. kW Palt = 2/3 * f0_target - 10.66. In Figure 10, the arrow represents the best compromise in terms of convenience and power consumed by the starter alternator 19.

FIG. 11 shows an example of a control-command device enabling the implementation of the method according to the invention for controlling the starting of the heat engine 11 while the vehicle is in an electric driving phase ensured by the electric motor traction 13. This control-command device can be integrated into a computer comprising for this purpose a memory storing software instructions for the implementation of the method for controlling the start of the heat engine 11.

This device comprises a hybrid train management module 32 receiving as input an SOC charge level of the battery 25 from a control system 33 of the traction battery 25.

As illustrated by FIGS. 11 and 12, following a request to start the heat engine 11, a module 34 makes it possible to determine, in a step 101, a number of top dead centers N_pmh before a first combustion according to a wheel torque Cr and the starting threshold S_mth of the heat engine 11 provided by the module. To this end, the module 34 integrates a map establishing a correspondence between these values.

Indeed, the number of top dead centers N_pmh is dependent on the torque at the wheel Cr during the restart of the engine 11, because the lower the torque at the wheel Cr at the time of the restart, the more the suspension of the powertrain will be able to filter the vibrations of the thermal engine 11. In fact, at high wheel torque Cr in electric driving (typically at low vehicle speed), starting will take place at three top dead points, whereas with a lower wheel torque (typically above 30 km/h), starting will take place at two top dead points. Thus, the angular acceleration of the crankshaft and the vibration level in the vehicle are correctly controlled while allowing the mechanical power delivered by the alternator-starter 19 to be as small as possible.

A module 35 makes it possible to determine, in a step 102, a power to be supplied to the heat engine 11 for its start-up as a function of the wheel torque Cr and of the start-up threshold S_mth of the heat engine 11 supplied by the module. To this end, the module 35 integrates a map establishing a correspondence between these values.

The control module 36 of the alternator-starter 19 controls, in a step 103, the alternator-starter 19 so that the alternator-starter 19 supplies the thermal engine 11 with the power Palt necessary for starting.

The control module 37 of the heat engine 11 controls, in a step 104, the starting of the heat engine 11 so that the first combustion of the heat engine 11 is controlled after the number of top dead centers previously determined.

Claims (10)

Method for controlling a start of a heat engine (11) belonging to a hybrid traction chain (10) installed on a train of a motor vehicle provided with wheels (17), said traction chain (10) also comprising an electric traction motor (13) and a reversible electric machine (19) coupled with the heat engine (11),
characterized in that, the motor vehicle being in an electric driving phase ensured by the electric traction motor (13) and a starting of the heat engine (11) being requested, said method comprises:
- a step (101) of determining a number of top dead centers (N_pmh) before a first combustion as a function of a wheel torque (Cr), and
- a step (104) for controlling the start of the heat engine (11) so that the first combustion of the heat engine (11) is controlled after the number of top dead centers (N_pmh) previously determined. Method according to Claim 1, characterized in that it comprises a step (102) of determining a power to be supplied to the heat engine (11) for its starting as a function of the wheel torque (Cr), and
- a step (103) for controlling the reversible electric machine (19) so that said reversible electric machine (19) provides the heat engine (11) with the power required (Palt) at start-up. Method according to Claim 2, characterized in that the number of top dead centers and the power to be supplied to the combustion engine (11) for its starting as a function of the wheel torque (Cr) are determined by also taking into account a starting threshold ( S_mth) of the heat engine (11). Method according to any one of Claims 1 to 3, characterized in that the number of top dead centers (N_pmh) before a first combustion is determined by means of a map (34). Method according to Claim 2, characterized in that the power to be supplied to the combustion engine (11) for its starting is determined by means of a map (35). Method according to any one of Claims 1 to 5, characterized in that the starting of the heat engine (11) is controlled over a period of between 500 and 650 ms. Method according to any one of Claims 1 to 6, characterized in that the electric traction motor (13) and the reversible electric machine (19) are powered by the same battery (25). Method according to claim 7, characterized in that in the case where the battery (25) is fully charged, a starting threshold of the heat engine (11) is between 7 kW and 9 kW. Method according to any one of Claims 1 to 8, characterized in that the electric traction motor (13) and the reversible electric machine (19) have an operating voltage of 48 Volts. Computer comprising a memory storing software instructions for implementing the method for controlling the start of a heat engine (11) as defined according to any one of the preceding claims.