Abstract:
The invention essentially relates to a method for optimising the recharging of a hybrid vehicle battery. When the clutch ( 10 ) is in the open position and/or when the gearbox ( 8 ) is in neutral, the heat engine ( 7 ) is at idling speed (W 1 ) by default when the charge status (SOC) of the high-voltage battery ( 19 ) is below a parameterisable threshold or a raised idling speed (W 2 ) when the charge status (SOC) of the high-voltage battery ( 19 ) is above the parameterisable threshold in order to increase the power generated by the first electrical machine ( 11 ) in order to recharge the battery.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a National Stage of International Application No. PCT/FR2010/052899, filed Dec. 23, 2010, which claims priority to French application 1050585, filed on Jan. 28, 2010. 
     
    
     BACKGROUND 
       [0002]    The invention relates to a method for optimizing the recharging of a hybrid vehicle battery. 
         [0003]    The invention has a particularly advantageous application in the domain of hybrid vehicles comprising a first axle driven by a combustion engine and a second electrically driven axle. 
         [0004]    The specific goal of the invention is to improve the availability of energy for the electrically driven axle, in particular when the vehicle operates in 4×4 mode. 
         [0005]    As know, hybrid vehicles comprise a combustion engine providing front wheel traction. For this purpose, a clutch ensures the connection between, on the one hand, the combustion engine and, on the other hand, the transmission connected with the front axle. The idle speed of this combustion engine is approximately 750 rev/min, when the clutch is disengaged and the transmission is in neutral. 
         [0006]    The engine is mechanically associated with an alternator/starter type front electrical machine. When driven by the combustion engine, this machine recharges the vehicle batteries (generator mode). This machine also starts the combustion engine when the machine operates in motor mode. In certain operating situations, this machine can also participate in providing traction to the vehicle. 
         [0007]    These vehicles also comprise an electrical machine providing traction to the rear axle via a gear box and a coupling device, for instance a dog clutch type device. In contrast to traditional 4×4 vehicles, the front axle traction and the rear axle traction are mechanically independent of each other. 
         [0008]    The front electrical machine and the rear electrical machine are connected to a high voltage battery through the intermediary of an electrical network. This high voltage battery is linked to the low voltage on-board network through the intermediary of a DC/DC converter. 
         [0009]    A brake control system is in general installed on the wheels of the vehicle. This system prevents blocking of the wheels and in case of need keeps the vehicle on its trajectory. 
         [0010]    When the driver selects 4×4 mode by means of a thumbwheel switch, the torque desired by the driver is distributed over the front axle and the rear axle of the vehicle. The torque available on the rear axle directly depends on the charge level of the battery. Indeed, the higher the charge level, the higher the maximum available torque because the discharge power of the battery is high. Inversely, the lower the charge level, the lower the available torque because the discharge power of the battery is low. 
       SUMMARY 
       [0011]    The specific goal of the invention is to propose a means for efficient recharging of the high voltage battery and for optimizing in this way the available torque in 4×4 mode. 
         [0012]    To this end, the idle speed is increased in order to increase the power available to the front machine and therefore the recharge power of the battery when the battery charge is less than an adjustable threshold between 10 and 50% of the maximum charge state. 
         [0013]    The idle speed returns to the default idle speed when the charge state of the battery returns above the adjustable threshold. 
         [0014]    The invention therefore relates to a method for optimizing the recharging of the battery of a hybrid vehicle comprising:
       a combustion engine mechanically associated with a first electrical machine,   a clutch installed between the combustion engine and the transmission connected to one of the axles of the vehicle,   a second electrical machine suitable for providing traction to the other axle of the vehicle,   a high voltage battery connected to both electrical machines,   the first machine is susceptible of being driven by the combustion engine when the first machine operates in generator mode to recharge the high voltage battery,
 
characterized in that when the clutch is disengaged and/or the transmission is in neutral:
   the combustion engine runs at the default idle speed when the charge state of the high voltage battery is lower than an adjustable threshold, or   a higher idle speed greater than the default idle speed when the charge state of the high voltage battery is greater than the adjustable threshold in order to increase the power generated by the first electrical machine to recharge the high voltage battery.       
 
         [0022]    According to an embodiment, the higher idle speed is about 10 to 40% higher than the default idle speed. 
         [0023]    According to an embodiment, the default idle speed is 750 rev/min. 
         [0024]    According to an embodiment, the higher idle speed is 950 rev/min. 
         [0025]    According to an embodiment, the adjustable threshold is about 10 to 50% of the maximum charge state of the high voltage battery. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The invention will be better understood by reading the following description and by examining the accompanying figures. These figures are provided as illustrative but non-limiting examples of the invention. They show: 
           [0027]      FIG. 1 : a schematic representation of a hybrid vehicle employing the method according to the invention; 
           [0028]      FIG. 2 : a graphic representation of the power supplied by the front machine (in Watt) as a function of the combustion engine speed (in rev/.min). 
       
    
    
       [0029]    Identical elements maintain the same references from one figure to another. 
       DETAILED DESCRIPTION 
       [0030]      FIG. 1  shows a hybrid vehicle  1  employing the method according to the invention comprising a front axle  2  and a rear axle  3  mechanically independent from each other. 
         [0031]    A conventional powertrain group  5  provides traction to the front axle  2  of the vehicle. More precisely, this group  5  comprises a combustion engine  7  connected to an electronic manual transmission  8  (BVMP) through the intermediary of a conventional clutch  10 , for instance, a dry or wet clutch. The transmission  8  is connected to the front axle  2  through the intermediary of a gear reduction (not shown). In a variant, the powertrain group  5  could comprise an automatic transmission  8 . 
         [0032]    The electrical machine  11  is mechanically associated with combustion engine  7 . When driven by the engine  7 , the electrical machine  11  operates in generator mode and supplies current to the high voltage battery  19  in order to recharge it. Machine  11  can also operate in motor mode to start the combustion engine  7 . In certain operating situations, machine  11  provides also traction to the front axle  2  by supplying torque (boost mode). 
         [0033]    In the case of very low temperatures and when machine  11  is not capable of providing the start function, a starter  13  is used to start the engine  7 . If necessary, a climate control system is mechanically connected with engine  7  and front machine  11 . 
         [0034]    Furthermore, an electrical machine  15  provides traction to the rear axle  3  of the vehicle. To this end, the machine  15  is connected to the rear axle  3  through the intermediary of a clutch  16  and a gear reduction assembly  17 . This clutch  16  consists, for instance, of a dog clutch, while the gear reduction assembly  17  has a single reduction ratio but in a variant could have several ratios. 
         [0035]    The two machines  11  and  15  are connected to each other through the intermediary of an electrical network. More precisely, machines  11  and  15  are connected to a high voltage battery  19  through the intermediary of an inverter  21  capable of cutting down the direct voltage of battery  19  to supply the electrical machines  11  and  15  when they operate in motor mode. When these electrical machines  11  and  15  operate in generator mode to recharge battery  19 , the inverter  21  is capable of transforming the alternating voltage produced by the machines  11  and  15  into DC voltage applied to the terminals of battery  19 . 
         [0036]    Battery  19  is connected to a DC/DC converter  20  which transforms the high DC voltage of battery  19  into a voltage suitable for starter  13  and for a low voltage battery  22  connected with the on-board network  24  of the vehicle. 
         [0037]    By preference, vehicle  1  is equipped with a conventional ESP or ABS type brake control system  25  which controls the braking forces in case of emergency braking, in order to ensure control of the trajectory of the vehicle and/or to avoid blocking of the wheels. 
         [0038]    A processor  28  commands the different control devices of the vehicle to achieve specifically the distribution of the torque Cg requested by the driver between the front axle  2  (torque Ccns_av) and the rear axle  3  (torque Ccns_ar). The requested torque Cg is calculated, by the module  29 , called driver intention interpretation module (IVC), specifically as a function of the travel of the accelerator pedal  31  and the speed V of the vehicle measured by a sensor  33  associated with a wheel. 
         [0039]    The clutch  1  and the transmission  8  communicate their respective states E E  and E B  to processor  28 . Battery  19  also communicates its charge state to the processor  28 . The driver selects the 4×4 operating mode of the vehicle by means of a thumbwheel switch  35 . In this operating mode the torque Cg will be divided approximately evenly between the front axle  2  and the rear axle  3  of the vehicle. 
         [0040]    As shown in  FIG. 2 , once the 4×4 mode is activated by the driver by means of the thumbwheel switch  35 , and when the processor  28  detects that clutch  10  is disengaged (E E =0) and/or the transmission  8  is in neutral (E B =0) and the charge state SOC is greater than an adjustable threshold, the engine  7  runs at the default idle speed W 1  which is in general 750 rev/min. This kind of operating situation can be observed when vehicle  1  is stopped and the combustion engine  7  is running. 
         [0041]    According to the invention, when processor  28  detects that clutch  10  is disengaged and/or that the transmission  8  is in neutral, and that the charge state SOC of the battery  19  is lower than the adjustable threshold, the operating point  38  of the combustion engine  7  is shifted, so that the engine runs at higher idle speed W 2 , greater than the default idle speed W 1 . In this way, the invention provides an increased speed of machine  11  when it is operating in generator mode to recharge battery  19 , and therefore improves the availability of energy in the electrically driven axle  2 . 
         [0042]    By preference, the higher idle speed W 2  is 10 to 40% higher than the default idle speed W 1 . 
         [0043]    Here, the speed W 1  is, for instance, approximately 950 rev/min, so that the power Pdisp available to recharge the battery  19  increases from 8 KW (for W 1 ) to 9 KW (for W 2 ), which corresponds with a 12% increase in available power Pdisp. 
         [0044]    As soon as the charge state SOC of battery  19  returns above the adjustable threshold, the operating point  39  of the combustion engine  7  is shifted back so that the idle speed of engine  7  returns from the higher speed W 2  to the default speed W 1 . 
         [0045]    In an example, the adjustable threshold is 10 to 50% of the maximum charge state of the high voltage battery  19 . 
         [0046]    The invention can also be employed when the vehicle is not operating in 4×4 mode in order to optimize the recharge of battery  19 . In this way, the invention can be employed when the vehicle  1  operates in thermal mode, in other words when only the combustion engine  7  provides traction to the vehicle.