Abstract:
The invention relates to a method for synchronising the common speed (ω p) of two concentric primary shafts ( 1, 6 ) of a hybrid transmission in a hybrid operating mode wherein said two shafts are rotatably connected by a first coupling means ( 5 ), with the speed (ω s) of a secondary transmission shaft ( 10 ) comprising at least one idler pinion for allowing the coupling of one of said pinions ( 11, 12 ) to the shaft ( 10 ) thereof by closing a second coupling means ( 13 ) that does not have mechanical synchronisation bodies, the torque (Te) of the electric machine being temporarily reduced during the synchronisation phase in order to meet the conditions of a perfect coupling when the value thereof caps at an upper limit value (T e   max ) or a lower limit value (T e   min ).

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to the field of the control of gear shifts in a gearbox. 
     More specifically, it relates to a method of and device for synchronizing the speed common to two concentric primary shafts of a hybrid transmission cumulatively receiving the torque from a combustion engine and the torque from an electric machine in a hybrid mode of operation in which these two shafts are rotationally connected by a first coupling means, with the speed of a secondary transmission shaft bearing at least one idler pinion. The synchronization proposed allows one of these pinions to be coupled to its shaft by closing a second coupling means that does not have mechanical synchronizing members. 
     This invention applies non-limitingly to a hybrid transmission for a motor vehicle provided with a combustion engine and with an electric drive machine, comprising two concentric primary shafts each bearing at least one gear transmitting to a secondary shaft connected to the wheels of the vehicle and a first means of coupling between two primary shafts that can occupy three positions, in which positions: the combustion engine is uncoupled from the drivetrain connecting the electric machine to the wheels, it drives the wheels with or without top-up from the electric machine, or it is coupled to the electric machine so that their torques can be combined. 
     Description of the Related Art 
       FIG. 1  describes a non-limiting example of a hybrid transmission using this design principle. This transmission, illustrated in publication WO2012/131259, comprises a solid primary shaft  1  connected directly by a filtration system (damping hub, damper, double fly wheel or the like)  2 , to the inertia flywheel  3  of a combustion engine (not depicted). The solid shaft  1  bears an idler pinion  4  that may be connected therewith by a first coupling system  5  (dog clutch, synchromesh, or other type of progressive or non-progressive coupling). A hollow primary shaft  6  is connected to the rotor of an electric machine  7 . The hollow shaft  6  bears two fixed pinions  8 ,  9 . It may be connected to the solid primary shaft  1  by means of the first coupling system  5 . A secondary shaft  10  bears two idler pinions  11  and  12 . The idler pinions  11 ,  12  may be connected to the primary shaft by way of a second coupling system  13  (dog clutch, synchromesh or other type of progressive or non-progressive coupling). The secondary shaft  10  also bears a fixed pinion  14  and a pinion  15  transmitting to a differential  16  connected to the wheels of the vehicle. 
     As indicated earlier on, the first coupling means  5  can occupy at least three positions in which:
         the combustion engine is uncoupled from the drivetrain connecting the electric machine  7  to the wheels (sliding gear in the middle as in  FIGS. 1, 2 and 3 ),   the combustion engine drives the wheels with or without top-up from the electric machine (sliding gear to the left), and   the combustion engine and the electric machine  7  are coupled in such a way that their respective torques are combined and sent to and the wheels (sliding gear to the right).       

     In hybrid mode (cf.  FIGS. 2 and 3 ), the electric machine drives the hollow primary shaft  6  whereas the solid shaft receives the torque from the combustion engine. The gearbox has two hybrid gear ratios referred to as “town” and “highway”, in which the torque is transmitted to the secondary shaft  10  via the fixed pinions  8  or  9  or no  7 . To shift from one of these two ratios to the other, the box has the second coupling system  13 . In the absence of synchronizing rings, a system that uses a dog clutch to couple the sliding gear with the pinions requires precise control of the primary speed by the electric machine and/or the combustion engine in order to avoid jerks in the flow of torque. 
     Publication FR 2 933 247 discloses a method for coupling a shaft of an electric machine with a wheel shaft for an electric or hybrid vehicle. The method described involves the following steps:
         the electric machine is fed a speed setpoint corresponding to the speed of the wheel shaft, disregarding the stepdown ratio between the shaft of the electric machine and the wheel shaft,   when the speed of the shaft of the electric machine reaches a calibratable threshold, a zero torque is applied to it and a mechanical synchronizing device is actuated so as to equalize the speed of the shaft of the electric machine with the speed of the shaft connected to the wheels, and   as soon as the speed of the shaft of the electric machine is equal to the speed of the shaft connected to the wheels (disregarding the stepdown ratio), dog-clutch engagement is performed.       

     With this method, the electric machine is made to operate first of all in order to reach a speed close, but not exactly equal, to that of the shaft connected to the wheels; a synchronizing device then completes the equalizing of the speeds between the two shafts, and then the speed ratio is finally engaged by dog-clutch engagement. 
     It has already been proposed for the idler pinions on a shaft of a gearbox without a mechanical synchronizing member to be synchronized by simply modulating the torque transmitted to these pinions so as to equalize their speed with the shaft prior to mechanical coupling. 
     However, in the case of a hybrid vehicle gearbox with concentric primary shafts driven by two power sources which are distinct, but connected to one another by a coupling means, the inertia caused by the machine during certain phases of the gear shift in hybrid mode, includes the combustion engine. The inertia to be overcome by the electric machine is then temporarily multiplied by a factor of ten, leading to torque saturations for this machine. 
     BRIEF SUMMARY OF THE INVENTION 
     The control strategy proposed has the object of making the phase of coupling the pinions to their shaft as transparent as possible. 
     To that end it seeks to provide desaturation of the torque of the electric machine in a way that is transparent to the driver, the torque demand of which needs to continue to be satisfied throughout the gear shift. 
     To this end, the invention plans for the torque of the electric machine to be temporarily reduced during the synchronizing phase so as to meet the conditions for perfect coupling when its value reaches a ceiling represented by an upper limit value or a lower limit value. 
     The corresponding device for that reason comprises at least two electric machine command torque desaturation units that allow the torque of the electric machine to be reduced temporarily during the synchronization phase in order to meet the conditions of perfect coupling in all circumstances. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The present invention will be better understood from reading the following description of one non-limiting embodiment thereof, with reference to the attached drawings in which: 
         FIGS. 1, 2 and 3  show the drivetrain of a hybrid transmission in neutral and in two of its hybrid gear ratios, 
         FIG. 4  describes the synchronizing device, 
         FIG. 5  is the regulator of  FIG. 4 , 
         FIGS. 6 and 7  show the first and second desaturator of  FIG. 4 , respectively, 
         FIG. 8  illustrates the results of the proposed method, and 
         FIG. 9  is another desaturation system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIG. 2 , the first coupling means  5  is closed in position  3 , so as to secure the solid shaft  1  to the hollow shaft  6 . The second coupling system  13  is closed, so as to secure the short-ratio idler pinion  12  and the secondary shaft  10 . The transmission is in hybrid mode on the short ratio. The contributions from the combustion engine and from the electric machine to the drivetrain combine. They are transmitted from the hollow primary shaft  6  to the secondary shaft by the descent of the pinions  8 ,  12 . 
     In  FIG. 3 , the first coupling means  5  is still closed, in position  3 , as in  FIG. 5 . The solid primary shaft  1  is therefore secured to the hollow primary shaft  6 . The second coupling system  13  is also closed: the idler pinion  11  of the intermediate gear ratio is secured to the secondary shaft  10 . The transmission is in hybrid mode on the intermediate gear ratio. The contributions of the combustion engine and of the electric machine to the drivetrain combine. 
     The desired synchronization is that of the speed  ω   p , common to the two concentric primary shafts  1 ,  6  cumulatively receiving the torque T ice  from the combustion engine and the torque T e  from the electric machine  7  in a hybrid mode of operation in which these two shafts are rotationally connected by the first coupling means  5 , with the speed  ω   s  of the secondary transmission shaft  10  which bears the idler pinions  11 ,  12 . It must allow one of these pinions to be coupled to its shaft  10  simply by closing the second coupling means  13 , which has no synchronizing members. 
     As indicated above, in the absence of mechanical synchronizing means, the synchronizing of the idler pinions  11  or  12  before they are coupled by dog clutches to the shaft  10  may be performed by adjusting the torque supplied by the electric machine. This is what is done during shifts between the two hybrid gear ratios, which are carried out with a break in torque by the dog-clutch coupling of the pinions  11  and  12  to the secondary shaft  10 . The main difficulties to be overcome in effecting these gear shifts are:
         that of following paths of the “ramp” type corresponding to the unfavorable case of heavy braking on a steep downward slope,   that of having sufficient static precision so that the speed discrepancy decreases very quickly down to around 30 revolutions per minute (a condition necessary for dog-clutch engagement to be carried out properly),   that of desaturating the electric torque as quickly as possible because in this phase the system is likely to become uncontrollable, and   that of eliminating the main sources of jerks in the flow of torque likely to be encountered during the coupling phase, thereby also avoiding bad wearing of the mechanical components of the coupling system.       

     If  ω   e  is the speed of the electric machine, T e  is the torque of the electric power source and J e  is the inertia of the electric machine, then the dynamics of the electric machine can be written as follows:
 
 J   e {dot over (ω)} e   =T   e   +T   de ,
 
in which expression T de  is the resistive torque of the electrical energy source, which is an unknown exogenic input.
 
     Similarly, the dynamics for the combustion engine can be written:
 
 J   ice {dot over (ω)} ice   =T   ice   +T   dice ;  (2)
 
where J ice : is the inertia of the combustion engine;  ω   ice  is the speed of the combustion engine;  ω   ice  is the speed of the combustion engine; T ice  is the torque of the combustion engine; and T dice  is the resistive torque of the combustion energy source, which is an unknown exogenic input.
 
     Given that, during the relevant gear shifts in hybrid mode,  ω   e = ω   ice = ω   p  (primary speed), it is possible to write:
 
( J   ice   +J   e ){dot over (ω)} p   =T   e   +T   ice   +T   dice   +T   de  
 
     In  FIG. 4 , ω p  is still the primary speed associated with the power sources, and ω s  is the speed of the secondary shaft connected with the wheels of the vehicle. The regulator receives as input the current value ω p  of the primary speed and the request for a synchronization speed equal to the secondary speed, disregarding the reduction ratio K, between the primary and secondary shaft in the hybrid operation. The regulator sends the electric torque setpoint T e  to the first limiter unit or limiter, which keeps the requested electric torque T e   appli  between T e   min , the minimum torque of the electric machine, and T e   max , the maximum torque of the electric machine. 
     The values T e   min  and T e   max  are sent respectively to the low desaturator ( 1 ) and to the high desaturator ( 2 ). In the event of low or high saturation of the electric torque signal T e , the desaturators send the combustion engine a torque setpoint T ice  that is limited by the second limiter between minimum and maximum values (T ice   min : the min torque of the combustion energy source and T ice   max : the max torque of the combustion energy source). The second limiter delivers the torque setpoint applied to the combustion engine, T ice   appli . 
     The device of  FIG. 4  comprises two desaturation units operating on the value of the torque T ice  supplied by the combustion engine. It allows the torque of the electric machine to be desaturated by activating the desaturation units  1  and  2 , so as to add a “desaturation” combustion torque to the electric machine when the torque T e  reaches a ceiling at its minimum value T e   min  (desaturator  1 ) or its maximum value T e   max  (desaturator  2 ). 
     This device reduces the electric torque, during the phase of synchronizing the speed of the primary shaft ω p  and that of the secondary shaft ω s , disregarding the stepdown ratio K, in order to meet the conditions for perfect coupling of a pinion  11  or  12  to the shaft  10 . 
     The regulator unit of  FIG. 5  compares the primary speed request with the primary speed ω p . An integral value of the difference is introduced into the calculation to eliminate static errors. In order to produce the reference signal T e , the signals generated by the integral action T e   int  and the proportional action T e   prop  are summed. 
     The torque T e  produced by the regulator unit of  FIG. 5  is then compared against the minimum torque T e   min  and against the maximum torque T e   max . 
     If T e ≦T e   min , the desaturator block  1  of  FIG. 6  (in which K p  and K i  are calibratable gains) is activated in such a way as to also provide retardation with the combustion engine until the torque T e  becomes higher than the minimum torque T e   min , producing a reference signal T ice . To produce this reference signal the signals generated by the integral action “T ice   int ” and the proportional action “T ice   prop ” (cf.  FIG. 6 ) are summed. 
     The torque of the electric machine  7  is thus reduced by influencing the value of the torque T ice  supplied by the combustion engine. 
     If T e ≧T e   min , the desaturation unit  2  of  FIG. 7  (in which K P  and K i  are also calibratable gains) is activated so as to also accelerate with the combustion engine until the torque T e  becomes lower than the max torque T e   max , producing a reference signal T ice . In order to produce this reference signal, the signals generated by the integral action T ice   int  and by the proportional action T ice   prop  are summed (see  FIG. 7 ). 
     In other words, the torque T e  of the electric machine is temporarily reduced during the synchronization phase in order to meet the conditions of perfect coupling when its value reaches a ceiling at an upper limit value T e   max  or a lower limit value T e   min . 
       FIG. 8  shows the time saving afforded by the invention in achieving synchronization. In this diagram it may be seen that the primary speed converges on the required value ω p   rq  at least one second earlier with the proposed strategy (curve  1 ) than in the absence thereof (curve  2 ). 
     The advantages offered by the method of the invention are many. Among these it may be noted that it complies with the inherent constraints on the box concerned, which are:
         the ability to follow “ramp” paths in steep descents, corresponding to the unfavorable instances of heavy braking,   having the required static precision so that the speed discrepancy very quickly falls into a range of 30 revolutions per minute, and   that the electric torque is desaturated as soon as possible because in this phase the system is susceptible to becoming uncontrollable.       

     Finally, it must be emphasized that the desaturation strategies generally applied in the control systems are of the “anti-windup” type, as may be that of  FIG. 9 , in which the discrepancy between the electric torque signal before and after limiting thereof is looped back into the regulator. 
     The big difference between the proposed strategy and this type of regulation is that the desaturation is not strictly software but rather the electric machine is desaturated using another source of power such as the combustion engine.