WO2012056135A1

WO2012056135A1 - Method of limiting the maximum torque that can be delivered or received by an electric machine powered by a battery and traction chain for hybrid vehicle implementing the method

Info

Publication number: WO2012056135A1
Application number: PCT/FR2011/052238
Authority: WO
Inventors: Florian Galinaud
Original assignee: Peugeot Citroën Automobiles SA
Priority date: 2010-10-28
Filing date: 2011-09-26
Publication date: 2012-05-03
Also published as: FR2966991B1; FR2966991A1

Abstract

Method of limiting the maximum torque that can be delivered or received by an electric machine (16) powered by a battery (18) and traction chain for hybrid vehicle implementing the method. The invention relates to a method of limiting the maximum torque that can be delivered or received by an electric machine powered by a battery and a traction chain for hybrid vehicle implementing the method. The method consists in: • determining (26) a temperature of the battery (18), • determining an activity indicator of the battery (18) representing the energy expenditure of the battery (18) during a time span, • determining a factor of limitation of the maximum torque as a function of the determined temperature and the determined activity indicator, - applying the limitation factor to the maximum torque that can be delivered by the electric machine (16) so as to obtain a value of limited maximum torque of the electric machine (16).

Description

Method for limiting the maximum torque that can be delivered or received by an electric machine powered by a battery and a traction chain for a hybrid vehicle implementing the method

The invention relates to a method of limiting the maximum torque that can deliver or receive an electric machine powered by a battery and a traction chain for a hybrid vehicle implementing the method.

[Ooo2] The invention is more particularly applicable to the field of hybrid vehicles that can be moved by two type n'énergie. These vehicles comprise at least two engines, for example thermal and electric. Both motors can be connected in parallel, in series or in power bypass. The combination of the two engines ensures the traction of the vehicle while optimizing energy efficiency in order to reduce energy consumption and pollution, especially for the engine. For example, parallel hybrid vehicles are able to drive independently through the thermal energy of the internal combustion engine or electrical energy of the electric traction machine. To do this, they are for example equipped with a set of a heat engine and a gearbox acting on the front end of the vehicle and an electric machine acting on the rear axle of the vehicle. [ooo3] An example of arrangement of elements participating in the motorization of such a vehicle is given in Figure 1. A front axle 10 receives mechanical energy produced by a heat engine 1 1 via a coupling device 12 and a gearbox 13. The coupling device 12 can be a dry clutch, wet or any other type. The gearbox 13 can be manual or automatic. The starting of the engine 1 1 is provided by a device 14 may for example be formed of a controlled starter or a more elaborate system such as those for stopping and restarting the engine when the vehicle goes through a phase where his speed is zero. This type of system is well known in the Anglo-Saxon literature under the name of "stop and start". For the traction of the vehicle, a rear axle 15 receives mechanical energy produced by an electric machine 16 by means of a coupling device 17. The electric machine receives electrical energy from a energy storage device such as a battery 18. [ooo5] Each element is controlled by a close control computer of its own. This function can be provided by the same computer common to several elements. The different computers are themselves controlled by a central computer called supervision that makes the decisions and synchronizes the actions to meet the will of the driver. The supervision computer function can be housed in an existing computer, such as for example a close calculator. The supervision computer controls the vehicle's drivetrain according to the external environment and the condition of the vehicle. He decides on the driving mode, coordinates all the transient phases and chooses the operating points of the various engines in order to optimize the fuel consumption, the depollution and the approval of the vehicle. The electric machine 16, linked to the rear axle, provides the necessary torque to advance the vehicle when the engine is stopped or in addition to it. More specifically, during the gearbox 13 ratio changes and the moment the front axle cancels its engine torque, the electric machine 16 applies a motor torque to partially or completely complete the torque break on the front axle. This strategy is called the "torque break compensation".

[ooo6] In all phases where the driver's torque will exceed the torque capacity of the engine 1 1 alone, the electric machine 16 provides a portion of the engine torque of the vehicle to increase the performance and amenity of this one.

[ooo7] Similarly, during deceleration phases of the vehicle, called the foot lift phase, or during the braking phases, the electric machine 16 provides a generator torque, opposing the advancement of the vehicle, to recover the kinetic energy of the vehicle and transform it into electrical energy stored in the battery 18. These different driving phases, using the electrical energy stored in the battery 1 8, charging as in discharge, lead to heating of it by Joule effect because of the internal resistance of the battery 1 8 In addition, the performance of the battery 1 8 falls at high temperature, leading to a significant deterioration of the benefits related to the electrical part of the hybrid powertrain. In addition, high temperatures damage the electrolytes of the battery 1 8 and significantly reduce its life.

The invention aims to improve limiting battery heating while maintaining maximum maximizing the electrical benefits available to the driver of the vehicle.

[Ooi o] For this purpose, the subject of the invention is a method for limiting the maximum torque that can be delivered or received by an electric machine connected to a battery, characterized in that it consists of:

• determine a battery temperature, • determine a battery activity indicator representing the energy expenditure of the battery over a period of time,

• determine a limiting factor of the maximum torque according to the determined temperature and activity indicator,

• apply the limiting factor to the maximum torque that can be delivered by the electrical machine to obtain a limited maximum torque value of the electrical machine.

[Ooi i] The invention limits the torque of an electric machine that can operate as a motor, when it delivers a torque, or as a generator, when it receives a torque. Indeed, in both modes of operation, the battery connected to the electrical machine is solicited by an electric current flowing through it.

The limiting factor can be determined from a table with two inputs, the temperature and the activity indicator and the table can be developed by simulation supplemented by tests. [0013] Advantageously, the activity indicator is a function of the current flowing in the battery (18).

The activity indicator is for example a function of the product of the current flowing in the battery (18) squared by the internal resistance of the battery. The internal resistance of the battery can be determined according to parameters such as battery temperature, the age of the battery and the state of health of the battery.

The activity indicator is advantageously filtered using a time constant depending on the determined temperature. It can also be filtered by gradient limitation.

[ooi 7] The temperature of the battery can be measured, simulated or determined according to the current flowing in the battery.

The invention also relates to a traction chain for a hybrid vehicle, the chain comprising an electric machine intended to provide a torque to the vehicle and a battery connected to the electric machine, characterized in that it further comprises a computer configured to implement the method according to the invention.

The invention will be better understood and other advantages will appear on reading the detailed description of an embodiment given by way of example, a description illustrated by the attached drawing in which:

FIG. 1, already described, schematically represents an example of arrangement of elements participating in the motorization of a hybrid vehicle,

FIG. 2 represents in block diagram form an example of a method, according to the invention, for limiting the maximum torque that can be delivered or received by an electrical machine.

It is understood that the invention is not limited to the arrangement shown in Figure 1. The invention can be implemented in any vehicle where all or part of the engine torque is obtained by means of an electric machine. The invention finds particular utility for hybrid vehicles having, in addition to the electric machine, another engine, for example thermal. The invention can be implemented regardless of the mode of association of the two motors: parallel, series or bypass. In such a vehicle, so that the driver does not feel the effects of the limitation of the torque delivered by the electric machine, the supervision computer can overcome the torque not supplied by the electric machine because of the limitation by an additional torque provided by the engine.

FIG. 2 represents in the form of a block diagram an exemplary method, according to the invention, for controlling the temperature of a battery 18 connected to an electric machine 16. The maximum torque that can be delivered or received by the electric machine can be a data supplied by the manufacturer of the machine in the form of a nominal torque. Tests or a simulation can also make it possible to know this data which is represented in block 21. A limiting factor between 0 and 1 is determined in block 22. This factor is multiplied, in block 23, by the maximum torque of the electric machine 18 to obtain, in block 24, a maximum limited torque that must not exceed electric machine 16. This maximum limited torque is for example used by the supervision computer to control the vehicle power train. At an initial time, the limiting factor is equal to 1 and the torque determined at block 24 is equal to the maximum torque from block 21. The torque of an electric machine depends on the current flowing through it. At first approach we can not distinguish the operating mode of the electric machine 16, engine or generator. Indeed, only the direction of the current changes and the effect on the temperature of the battery 18 is identical. It is of course possible to limit the maximum torque differently according to the operating mode of the electric machine 16. The function between torque and current is substantially a proportionality relation. It is possible to refine this function by tests.

To simplify the understanding of the invention, it is assumed that the current flowing in the electrical machine 16 is equal to the current flowing in the battery 18. For example, if we implement a synchronous electric machine powered by DC current and controlled by an inverter, only the direct current supplying the machine will be considered. The determination of the current flowing in the battery is done in block 25. This determination can be made by a measurement of current or by calculation from a torque setpoint applied to the electric machine. This setpoint is for example determined by the supervision computer according to the wish of the driver of the vehicle. This setpoint can not normally exceed the maximum torque determined in block 24.

Two parameters are used to limit the maximum torque of the electrical machine 16. First, the temperature of the battery 18 shown in block 26. This temperature can be measured by a temperature sensor or calculated from the current flowing in the battery 18. This calculation is made in block 27 and takes into account the heating of the battery 18 which is a function of losses Joule effect in the battery 18, its thermal inertia and the heat dissipation with the external environment. The Joule losses are a function of the current flowing in the battery 18, determined in block 25.

Another parameter used to limit the maximum torque of the electric machine 16 is an indicator of activity of the battery 18 representing the energy expenditure thereof and more specifically the energy expenditure by Joule effect of the battery during a range. of time. This indicator is determined in block 28. It is linked to the temperature variations of the battery 18. It would be possible to simply calculate the derivative of the temperature with respect to time from several temperature measurements distributed over time to obtain information. similar to the activity indicator. But a better prediction of the evolution of the temperature of the battery 18 is obtained by building the activity indicator from the heat dissipated in the battery 18 during its operation. The indicator can be determined from the current determined in block 25. This indicator is a function of the internal resistance of the battery 18. It is for example equal to the product of the current squared by the internal resistance of the battery 18. internal resistance of the battery 18 may vary depending on the environment thereof. The value of the internal resistance can be measured, or determined according to several parameters such as the battery temperature 18, the age of the battery 18 and the state of health of the battery 18. For use embedded in a vehicle automobile, the age of the battery 18 is the distance traveled by the vehicle since the installation of the battery 18. The state of health of the battery, well known in the English literature as the State of health ( SOH) is an indicator that can be delivered by an electronic device integrated with the battery 18. This indicator is a function of the history of use of the battery 18, such as the number and magnitude of charges and discharges incurred by the battery. battery 18. The determination of the internal resistance can be made from simulations or tests taking into account the different parameters described above.

The limiting factor is determined, in block 22, by means of a table with two inputs formed by the two parameters, temperature and activity indicator. When the temperature is low and the activity is low, no limitation is necessary and the limiting factor is 1. When the temperature is low and the activity is high, an average limitation is necessary. When the temperature is high and the activity is low, an average limitation is necessary. When the temperature is high and the activity is strong, a strong limitation is necessary. Limiting factors vary continuously with temperature and activity indicator. Limit factor values can be developed by simulation. This simulation is usually completed by road tests of the vehicle. It is possible to refine the entry in the table corresponding to the activity indicator by filtering, in block 29, the indicator determined at block 28 before entering the table of block 22. This filtering is for example of low pass type and its time constant, determined in block 30, is a function of the temperature determined in block 26. For example, the higher the temperature, the more the time constant is reduced. The values of the time constant can be developed by simulation that can be supplemented by road tests of the vehicle. It is also possible to complete this filtering with a gradient limiter filter. More precisely, the variation in the time of the activity indicator is limited. If it is expressed in Joules, it can for example limit its variation to 10 Joules per second. This maximum gradient value can be adapted, as for the time constant, as a function of road tests of the vehicle. The filtering makes it possible to integrate the instantaneous energy dissipated in the battery over a given period of time. The method of the invention can be implemented in a computer belonging to the drive train of the hybrid vehicle. More specifically, the maximum limited torque can be determined in a close control computer specific to the electric machine. In this case, the limited torque information must be transmitted to a supervision computer in order to control the entire vehicle power train. It is also possible to implement the method of the invention directly in the supervision computer.

A control feature of hybrid vehicles comprising a heat engine and an electric traction machine is to compensate for the absence of engine torque delivered by the engine during gear changes gearbox associated with the engine. The supervision computer can compensate for this momentary absence of torque by using the electric machine. By implementing the method of the invention, even if the maximum torque of the electric machine is limited, it is possible to accept a one-time overshoot of this limitation for such compensation. Indeed, this type of compensation is of short duration and the thermal inertia of the battery makes it possible to accept it, all the more easily as the process of the invention will very quickly lead to a greater limitation of the maximum torque, for example because of the filtering and the time constant determined at blocks 29 and 30. It is of course possible to authorize such an overrun for other transient situations defined by the supervision computer.

More generally, the applicant has realized that the determination of the limitation of the torque of the electric machine is much more effective than a determination solely based on the temperature of the battery. In other words, by implementing the invention, the maximum temperature that we do not want to exceed for the battery is much less often achieved than with a torque limitation solely based on the temperature of the battery.

Claims

1. A method of limiting the maximum torque that can deliver or receive an electric machine (16) connected to a battery (18), characterized in that it consists of:

Determining (26) a temperature of the battery (18); • determining (28) a battery activity indicator (18) representing the energy expenditure of the battery (18) over a time period;

Determining (22) a maximum torque limiting factor as a function of the determined temperature (26) and activity indicator (28),

• apply the limiting factor (22) to the maximum torque (21) that can be delivered by the electrical machine (16) to obtain a limited maximum torque value (24) from the electrical machine (16).

Method according to claim 1, characterized in that the limiting factor (22) is determined from a two input table, the temperature (26) and the activity indicator (28).

3. Method according to claim 2, characterized in that the table is developed by simulation supplemented by tests.

4. Method according to one of the preceding claims, characterized in that the activity indicator (28) is a function of the current (25) flowing in the battery (18).

5. Method according to claim 4, characterized in that the activity indicator (28) is a function of the product of the current (25) flowing in the battery (18) squared by the internal resistance of the battery (18) .

6. Method according to claim 5, characterized in that the internal resistance of the battery (18) is determined according to parameters such as the battery temperature (18), the age of the battery (18) and the state health of the battery (18).

7. Method according to one of the preceding claims, characterized in that the activity indicator (28) is filtered (29) using a time constant (30) depending on the determined temperature (26).

8. Method according to one of the preceding claims, characterized in that the activity indicator (28) is filtered (29) by gradient limitation.

9. Method according to one of the preceding claims, characterized in that the temperature (26) of the battery (18) is determined according to the current (25) flowing in the battery (18).

A traction chain for a hybrid vehicle, the chain comprising an electric machine (16) for providing torque to the vehicle and a battery (18) connected to the electric machine (16), characterized in that it further comprises a computer configured to implement the method according to one of the preceding claims.