Abstract:
A method for controlling recharging of a traction battery on a motor vehicle hybrid transmission including a heat engine and at least one electrical machine, wherein the electrical machine is used as a sole motor-driven power source up to a speed threshold beyond which it is possible to couple the heat engine with the wheels, in hybrid modes, to run power supplies from the heat engine and the electrical machine simultaneously with each other. In the method, below the speed threshold, the electrical machine ensures only torque to be transmitted to the wheels, while the heat engine is ignited to provide recharging without contributing to pull of the vehicle when a driver bears on the accelerator pedal, and while the wheels are separate from the heat engine and the electrical machine, when the driver does not bear on the accelerator pedal, to enable recharging of the battery.

Description:
BACKGROUND 
     The present invention concerns the field of hybrid transmissions for motor vehicles comprising on the one hand a driving heat engine and on the other at least one electrical machine. 
     More precisely, the invention relates to a method for controlling recharging of the traction battery on a hybrid transmission for a motor vehicle equipped with a heat engine and at least one electrical machine, where the electrical machine is used as the sole motor-driven power source up to a speed threshold beyond which it is possible to couple the heat engine with the wheels, in hybrid modes, so as to run the power supplies from the heat engine and the electrical machine simultaneously with each other. 
     This invention can be applied in a non-limiting manner to a hybrid transmission for a motor vehicle equipped with a heat engine and a driving electrical machine, comprising two concentric primary shafts each bearing at least one reduction gear on a secondary shaft connected to the wheels of the vehicle and a first coupling means between two primary shafts, said coupling means being able to occupy three positions. 
       FIG. 1  describes a non-limiting example of a hybrid transmission having this principle of construction. This transmission comprises a solid primary shaft  1  connected directly by means of a filtration system (shock absorber means, “damper”, dual mass flywheel or other)  2  to the flywheel  3  of a heat engine (not shown). The solid shaft  1  carries an idler gear  4  able to be connected thereto by a first coupling system  5  (clutch, synchronizer, or other type of coupler, which may or may not be progressive). A hollow primary shaft  6  is connected to the rotor of an electrical machine  7 , preferably (but not obligatorily) of the axial, disk-shaped machine type. Other types of electrical machine can also be used within the scope of the invention, for example radial machines, having an excitation magnet or coil, or reluctance machines. The hollow shaft  6  carries two fixed gears  8 ,  9 . The hollow shaft  6  may be connected to the solid primary shaft  1  by means of the coupling system  5 . A secondary shaft  10  carries two idler gears  11  and  12 . The idler gears  11 ,  12  can be connected to the primary shaft by means of a second coupling system  13  (clutch, synchronizer, or other type of coupler, which may or may not be progressive). The secondary shaft  10  also carries a fixed gear  14  and a reduction gear  15  toward a differential  16  connected to the wheels (not shown) of the vehicle. 
     As indicated above, the first coupling means  5  may occupy at least three positions, in which:
         the heat engine is decoupled from the kinematic chain connecting the electrical machine  7  to the wheels (position  1 ),   the heat engine drives the wheels with or without the contribution of the electrical machine (position  2 ), and   the heat engine and the electrical machine  7  are coupled so as to add together the respective torques thereof in the direction of the wheels (position  3 ).       

     In the hypothesis in which, by construction, a vehicle equipped with such a transmission cannot use the heat engine to contribute to the pull of the vehicle below a speed threshold, the battery is primarily discharging at the low speeds of the vehicle. Beyond the speed threshold, the energy management system of the vehicle is capable of distributing the power between the heat engine and the electrical machine so as to ensure a minimum autonomy of the vehicle in electric mode. When the vehicle travels regularly below the speed threshold, there is the problem of providing an energy reserve in the battery in all circumstances so as to ensure at least the launching of the vehicle until the heat engine is started. Without this reserve of electrical energy, the vehicle is necessarily immobilized in a “roadside recharging mode”, in which the heat engine recharges the vehicle battery at standstill before the battery has sufficient energy to re-launch the vehicle. 
     BRIEF SUMMARY 
     The object of the present invention is to overcome the disadvantage of immobilizing the vehicle roadside in order to recharge the battery. 
     With this objective, the invention proposes that, below a speed threshold, the electrical machine ensures only the torque to be transmitted to the wheels, whereas the heat engine is ignited so as to provide recharging without contributing to the pull of the vehicle when the driver presses on the accelerator pedal, while the wheels are decoupled from the heat engine and from the electrical machine when the driver does not press on the accelerator pedal. 
     In addition, when the driver presses on the brake pedal or completely releases the accelerator pedal, neither the electrical machine nor the heat engine contribute to the pull. They are then used to activate the recharging mode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The present invention will be better understood upon reading the following description of a non-limiting embodiment thereof, with reference to the accompanying drawings, in which: 
         FIG. 1  illustrates the regeneration of the traction battery of a vehicle on a hybrid transmission in neutral, 
         FIGS. 2 to 7  illustrate the different possibilities for operation of this transmission, and 
         FIGS. 8 and 9  illustrate the implementation of the method on the described transmission. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIG. 1 , the first coupling system is in position  3 , as in  FIGS. 5 and 6 , that is to say it connects in rotation the solid primary shaft  1  and the hollow primary shaft  6 . The second coupling system  13  is open. The transmission  17  is thus in “neutral”. The turning heat engine can drive the traction electrical machine, thus functioning as a generator to recharge the batteries of the vehicle at standstill. 
     In  FIG. 2 , the first coupling system  5  is open (position  1 ), whereas the second coupling system  13  is closed so as to interlock the idler gear of the short ratio  12  with the secondary shaft  10 . The transmission is in electric mode at the short ratio, or first ratio of forward drive. 
     In  FIG. 3 , the first coupling system  5  is still open (position  1 ), whereas the second coupling system  13  is closed, so as to interlock the idler gear of the intermediate ratio  11  with the secondary shaft  10 . The transmission is in electric mode at the intermediate ratio, or second ratio of forward drive. 
     In  FIG. 4 , the first coupling system  5  is closed in position  2 , so as to interlock with the solid shaft  1  the idler gear  4  carried thereby, whereas the second coupling means  13  is open. The transmission is at the long ratio, or third ratio. The electrical machine does not provide torque. 
     In  FIG. 5 , the first coupling means  5  is closed in position  3 , so as to interlock the solid shaft  1  and the hollow shaft  6 . The second coupling system  13  is closed so as to interlock the idler gear of the short ratio  12  and the secondary shaft  10 . The transmission is in hybrid mode at the short ratio. The contributions of the heat engine and of the electrical machine to the traction chain are combined. They are transmitted from the hollow primary shaft  6  to the secondary shaft by the reduction gears  8 ,  12 . 
     In  FIG. 6 , the first coupling means  5  is still closed, in position  3 , as in  FIG. 5 . The solid primary shaft  1  is thus interlocked with the hollow primary shaft  6 . The second coupling system  13  is also closed: the idler gear  11  of the intermediate ratio is interlocked with the secondary shaft  10 . The transmission is in hybrid mode at the intermediate ratio. The contributions of the heat engine and of the electrical machine to the traction chain are combined. 
     In  FIG. 7 , the first coupling system  5  is closed in position  2 : it interlocks with the solid primary shaft  1  the idler gear  4  carried thereby. In addition, the second coupling means  13  is closed so as to interlock the idler gear  11  of intermediate ratio with the secondary shaft  10 . The transmission is in hybrid mode at the long ratio, with combining of the contributions of the heat engine and of the electrical machine. 
     The proposed strategy for controlling the recharging mode of the battery is preferably implemented below an energy threshold S1 and is deactivated above a threshold S2&gt;S1 of the battery. In addition, it takes into account a speed threshold V of the vehicle, which may correspond to the threshold of engagement of the heat engine for participation in the pull. The control of the recharging of the battery is different in a low speed zone (ZEV), that is to say below the threshold V, and in a high speed zone, that is to say above the threshold V. 
     At low speed, it is not possible to act on the points of operation, and the electrical machine ensures only the torque to be transmitted to the wheels. The heat engine is ignited to provide recharging, but does not contribute to the pull of the vehicle. When the driver presses on the accelerator pedal (without touching the brake pedal), the kinematic chain of the transmission is that of  FIG. 2 . 
     When the driver does not press on the accelerator pedal (foot lifted) or when he presses on the brake pedal, the transmission is in the configuration of  FIG. 1  (recharging mode). The wheels are decoupled from the traction elements (engine and machine). The point of operation is defined by acoustic constraints and by the minimization of the consumption. For acoustic reasons, the range of operation of the heat engine is reduced (that is to say it cannot exceed a speed of rotation). 
     At high speed, the heat engine ensures the torque to the wheel and an addition, which the electrical machine will draw to recharge the battery. The kinematic chain may be the same with and without pressure on the accelerator pedal. The quantity of torque drawn to recharge the battery is selected to minimize the following function:
 
 H _ eq =thermal consumption(engine torque,engine speed)+ s ×electricity consumption(machine torque,machine speed),
 
in which H_eq is the total quantity of energy consumed and s is the equivalence factor, which gives the correspondence between the electrical energy with the mechanical energy (for example between 1 kWh and the equivalent thereof in grams of fuel). The speeds of the heat engine and of the electrical machine are imposed by the speed of the vehicle and the mode of coupling of the transmission, which means that the strategy adapts depending thereon. The equivalence factor “s” favors the recharging of the battery when the strategy is activated. The functions of thermal consumption and electricity consumption are consumption mappings obtained on test benches. The kinematic chain selected is that of the “town hybrid” mode of  FIG. 5 , that of the “road hybrid” mode of  FIG. 6 , or that of the “motorway hybrid” mode of  FIG. 7 , depending on the speed of the vehicle, that is to say that of one of the usual hybrid modes of the vehicle. The strategy consists of choosing the torque distribution for minimizing the function H_eq:
         at high speed, when the recharging strategy is not activated, the equivalence factor is selected to minimize the overall energy consumption; within acceptable limits it is in fact possible to adapt the torque and the heat engine speed to find the best point of operation of the transmission, taking into account the output of the electrical machine and of the heat engine; when the recharging strategy is activated the equivalence factor is selected such that it favors the recharging of the battery,   at low speed, when the recharging strategy is not activated, the electrical machine ensures only the pull, the heat engine is switched off and when the driver releases the accelerator or presses on the brake the kinematic mode remains that of  FIG. 2  in order to recover the kinetic energy of the deceleration; when the recharging strategy is activated the electrical machine ensures only the pull, the heat engine is ignited and when the driver releases the accelerator or presses on the brake the kinematic mode remains that of  FIG. 1  to recharge the battery via the heat engine.       

     When the driver passes to neutral, at low and high speed, the control is the same as when pressing on the brake at low speed: pass into recharging mode and minimization of the function H_eq depending on the engine speed and torque whilst observing the acoustic constraints, the wheels being decoupled from the heat engine and from the electrical machine. 
       FIGS. 8 and 9  illustrate the implementation of the invention on the transmission described above. The speed threshold V is, for example, 16 kilometers per hour if this speed corresponds to the coupling threshold of the heat engine. This threshold can be that which is retained more generally in a mode of use of the vehicle referred to as prolongation of autonomy or “long range”, in which the heat engine is connected after electrical start as soon as the speed allows (at 1500 revolutions per minute, for example at 16 Km/h). The two first ratios then become hybrid, and the electrical machine is essentially used in regeneration. These two hybrid modes “town” (see  FIG. 5 ), when the speed of the vehicle is above speed threshold V and below a first speed V1, and “road” (see  FIG. 6 ), when the speed of the vehicle is above the first speed V1 and below a second speed V2, are supplemented, if desired, by the third hybrid mode “motorway” of  FIG. 7 , when the speed of the vehicle is above the second speed V2. 
       FIG. 8  shows two separate values S1 and S2 of the state of charge (SOC) of the battery for the activation threshold when the current state of charge is lower than S1 and for the deactivation threshold S2 when the current state of charge is greater than S2. As indicated above, the transmission, at low speed, has two different configurations below and above the activation threshold. By contrast, it no longer changes state in accordance with the state of charge of the battery beyond the threshold V, in the three hybrid modes thereof, but benefits from a targeted control, favoring recharging below the activation threshold and favoring reduced consumption above said threshold by the choice of a suitable equivalence factor. 
     In conclusion, the control method proposed by the invention makes it possible to recharge the battery during travel in a coherent operating mode referred to as the “non-stop recharging mode”, which makes it possible to prevent the immobilization of a hybrid vehicle in order to recharge the battery when the vehicle does not have the possibility to launch and move at low speeds on the heat engine alone. In this case, it is possible to use the vehicle in a specific mode to recharge the battery during travel. This method is applicable to any transmission of the type described above and to a vehicle equipped with such a transmission, but also to any other transmission and any other hybrid vehicle of which the construction does not make it possible to drive the vehicle by the heat engine over a speed range.