Abstract:
An infinitely variable transmission with power shunting having at least two operating modes, whereof the components are distributed between two power paths connecting in parallel the heat engine to the vehicle wheels, including at least three planetary gear trains, two electrical machines, at least one reduction stage, and a control distributing differently the power between the two power paths based on the operating mode thereof.

Description:
BACKGROUND OF THE INVENTION 
   I. Field of the Invention 
   The present invention relates to a power-splitting transmission, by means of which there can be achieved a continuous variation from reverse gear to forward gear, passing through a particular position referred to as “neutral engaged”, wherein the travel speed of the vehicle is zero for any speed whatsoever of the internal combustion engine. 
   More precisely, its object is a power-splitting infinitely variable transmission on the basis of an electric variator and of a compound gearset, plus adjusting means that distribute the power between the input and output of the transmission differently depending on the mode of operation thereof. 
   II. Description of Related Art 
   Power-splitting transmissions can be based on three known principles or modes of power splitting. According to the first mode, known as “coupled-input”, the transmission is provided with a pair of power-splitting pinions for splitting the power at the input of the mechanism, and with an “assembler” epicyclic gearset, which recombines the powers at the output of the mechanism. The control element is a variator. 
   In power-splitting transmissions of the “coupled-output” type, there is provided, for example, a power-dividing planetary gearset at the input of the mechanism and a power-reassembling pair of pinions at the output of the mechanism, the control element again being a variator. 
   Finally, in power-splitting transmissions of the “two matching points” type, a first power-dividing epicyclic gearset can be placed at the gearbox input while a second power-reassembling epicyclic gearset is disposed at the gearbox output, the control element again being a variator. 
   The traditional infinitely variable transmissions (I.V.T.) use only one or two of these three operating principles. 
   From U.S. Pat. Nos. 5,558,589 and 5,935,035 there are known infinitely variable transmissions with two modes of operation combining at least two planetary gearsets, two mode-changing clutches and one electric variator, using the coupled-output power-splitting principle as the first mode of operation. 
   According to these patents, the mode-changing means are disposed outside the epicyclic gearsets. 
   The merit of having two modes of operation available lies in the increased range of transmission ratios and in the possibility of reducing the size of the electric variator, which can be composed on the basis of electric machines. 
   Nevertheless, in these known two-mode architectures, the mode changes are effected by multiple-disk clutches disposed on the output of the transmission, and for this reason are accompanied by torque jolts that are sensed as unpleasant by the users. 
   Another disadvantage of the architectures described in these patents lies in their complexity, in particular related to the presence of at least two clutches and one brake. 
   In previous French Patent Application 01-04690 in the name of the same Applicant, there was described a power-splitting infinitely variable transmission with two modes of operation, wherein the architecture is simpler than in the traditional transmissions of the same type, electric machines of small dimensions are used, and the mode changes thereof are not accompanied by any torque jolt. In this French Patent Application 01-04690, the mode changes are effected by acting on internal mechanical links of the transmission situated between the two gearsets. For this purpose, two reducing stages are disposed between the two epicyclic gearsets, these stages being respectively utilized in the first and in the second mode of operation. These two reducing stages are disposed in parallel between the gearsets on the same power train. 
   Application of these prior art teachings poses the problem of an infinitely variable transmission (I.V.T.) that is sufficiently compact that it can be disposed easily in a motive power unit of a vehicle. 
   In addition, such an infinitely variable transmission is difficult to use with an internal combustion engine that produces high torque and power, and it cannot be easily matched to the type of engine, whether it be gasoline or diesel. 
   The prior art leads to design problems for the hydraulic actuation circuit, which then poses major problems during repair and maintenance of the gearbox, particularly in the case in which the mode-changing system is constructed in the form of a multiple-disk clutch. 
   In the case in which the mode-changing system is provided with mechanical gearbox claws, there are problems for exchanging the mode-changing system inside the gearbox. 
   Finally, the matching of such a gearbox to a gasoline-powered internal combustion engine also poses a problem related to the speeds of rotation, which are very high, thus imposing large mechanical stresses on certain spinning elements. 
   In fact, the engine speeds of a gasoline engine are higher than those of a diesel engine, in such a way that certain elements of the gearbox spin very rapidly. 
   The problem posed by the rapid rotation of a gear part will be seen in particular in the description hereinafter. 
   BRIEF SUMMARY OF THE INVENTION 
   These disadvantages of the prior art can be remedied by the present invention. 
   In particular, it consists in proposing a means by which space can be left for the electric variator. 
   The mode-changing system can be disposed on the periphery of the gearbox, in such a way that it can be adjusted more easily by means of hydraulic actuators or electromechanical actuators. 
   Finally, the operating speeds of the gearbox can be reduced by the adopted transmission structure. 
   To this end, the present invention relates to a power-splitting infinitely variable transmission, which is provided with a primary power train composed of two epicyclic gearsets connected by a compound gearset having two connections. 
   By virtue of such a structure, it has therefore been possible to replace the two reducing stages and the simple gearset of the prior art by an assembly composed of two reducing stages and a compound gearset. 
   The present invention also relates to a power-splitting infinitely variable transmission with two modes of operation, wherein the constituent elements of are distributed between two power trains connecting the internal combustion engine in parallel manner to the wheels of the vehicle, these means including two epicyclic gearsets, two electric machines, one reducing stage and adjusting means that distribute the power between the two power trains differently depending on the mode of operation thereof. This infinitely variable transmission is provided with a third epicyclic gearset in series with one of the two epicyclic gearsets on one of the two power trains, the said third epicyclic gearset cooperating with the said adjusting means in such a way that, in a first mode of operation, all elements of the third gearset are spinning at the same speed. 
   The invention also proposes that the infinitely variable transmission be provided with a first compound gearset by means of which the internal combustion engine can be connected to the wheels of the vehicle according to a main power-splitting train and with a simple gearset by means of which power splitting can be achieved as well as with a compound gearset in such a way as to achieve a system for changing mode between at least two modes of operation of the infinitely variable transmission. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other characteristics and advantages of the present invention will be better understood by means of the description and of the attached figures, wherein: 
       FIG. 1  and  FIG. 2  are basic diagrams describing the prior art on which the present invention is based; 
       FIGS. 3 and 4  are respectively a basic diagram and a mechanical layout diagram of the infinitely variable transmission of the invention; 
       FIGS. 5 and 6  are respectively a basic diagram and a kinematic diagram of a preferred embodiment of the present invention; 
       FIG. 7  is another basic diagram of the present invention; 
       FIG. 8  is a kinematic diagram of a mechanical embodiment of the invention illustrated in  FIG. 7 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates the basic diagram of the infinitely variable transmission of French Patent Application 01.04690. 
   The transmission of  FIG. 1  is composed of two epicyclic gearsets  5 ,  6 , seven reducing stages  7 , two mode-changing systems  8  and  9 , which can be either claw couplings or multiple-disk clutches, and two electric machines  2 ,  4 , together comprising a variator. 
   This transmission has four input and output connections, which can be connected respectively to internal combustion engine  1 , to wheels  3  and to the two electric machines  2  and  4 . 
   Internal combustion engine  1  is connected to a reducing stage  1 ′. Wheels  3  are connected to two reducing stages  3 ′. A first electric machine  2  of the variator is connected to a reducing stage  7  and a second electric machine  4  is connected to a reducing stage  4 ′ and to two mode-changing systems  8  and  9 . 
   Three reducing stages are connected to first epicyclic gearset  5 . Four reducing stages are connected to second epicyclic gearset  6 . One reducing stage  8 ′ or  9 ′ is connected to each of the mode-changing systems  8  and  9 . 
   The transmission illustrated by  FIG. 1  is therefore provided with seven reducing stages, five of which are disposed between the two epicyclic gearsets and two of which are disposed outside these said gearsets. 
   Internal combustion engine  1  is connected to epicyclic gearset  5  via a reducing stage  1 ′, and wheels  3  are connected to each epicyclic gearset  5 ,  6  via a reducing stage  3 ′. 
   This transmission has two modes of operation with two matching points. In the first mode, first mode-changing system  8 , connected to the reducing stages on the one hand and to an electric machine  4  on the other hand, is open. This first branch is therefore free, whereas the second, containing second mode-changing system  9 , connected just as the first to two reducing stages and to electric machine  4 , is closed. 
     FIG. 2  illustrates a practical mechanical embodiment of the basic diagram of  FIG. 1 . 
   In  FIG. 2 , internal combustion engine  100  is connected to a central shaft  101 , which traverses the entire mechanism of the gearbox, whose pinions and epicyclic gearsets have been represented schematically. 
   The electric variator is composed essentially of a first electric machine  102  and of a second electric machine  103 . 
   Electric machines  102  and  103  can function equally well as motors or generators and are preferably connected to an electrical energy storage element such as a battery and/or a high-value capacitor. 
   Finally, the gearbox is connected via a differential  105  to wheels  104  of the vehicle. 
   The gearbox or infinitely variable transmission of the invention is provided essentially with a first epicyclic gearset  111  and a second epicyclic gearset  116 . 
   It is also provided with a mode-changing system  106 . 
   Planet carrier  112  is mounted to rotate freely around traversing central shaft  101  by means of a suitable bearing. The planet gears of planet carrier  112  are disposed in such a way that they can be coupled on the one hand to sun gear  114 , which is integral with shaft  101 , and on the other hand to ring gear  113 , which spins freely around a bearing disposed on traversing shaft  101 . 
   Planet carrier  112  of first epicyclic gearset  111  is driven by an external toothing by means of a chain  110  connected to a pinion  109  integral with the output shaft of first electric machine  102  of the electric variator. 
   Ring gear  113  of the first epicyclic gearset has an external toothing  122 , which meshes with a driving pinion  121  of differential  105  connected to wheels  104 . 
   The coupling of toothing  122  and pinion  121  produces a reducing stage  3 ′. 
   Second epicyclic gearset  116  is provided with a ring gear  117 , a first toothing of which is coupled by a chain  115  to a pinion  108  driven by mode-changing system  106 . 
   Sun gear  119  of second epicyclic gearset  116  is provided with an internal toothing and an external toothing. 
   The internal toothing of sun gear  119  is coupled to the planet gears of planet carrier  118 , while the external toothing of sun gear  119  is connected to a driving pinion  120  of second electric machine  103  of the electric variator of the infinitely variable transmission. 
   Ring gear  117  also has an external toothing, which is coupled to another pinion  107  adjusted by mode-changing system  106 , in such a way that the output shaft of first electric machine  102  can be coupled selectively either to pinion  107  or to pinion  108 . Mode-changing system  106  is implemented:
         either by means of claw couplings activated by a suitable drive system;   or by two clutches activated by suitable actuators.       

   This change of mode makes it possible to introduce two different reduction ratios K 5  and K 6  depending on whether the mode-changing system activates pinion  108  or pinion  107  and also to implement two different power pathways or trains in order to achieve a two-mode infinitely variable transmission. 
     FIG. 3  illustrates the basic diagram of the present invention. 
   The infinitely variable transmission of the present invention is provided with a primary power train and a secondary power-splitting train. 
   For the purpose of constructing such a structure, internal combustion engine  130  is connected via a reducing stage  136  to ring gear C 2  and to planet carrier ps respectively of a first epicyclic gearset  137  and of a second epicyclic gearset  138  of gearbox  134  proper. 
   Vehicle wheels  133  are connected to gearbox  134  via a reducing stage  139  of gear ratio K 0 , one access of which is coupled respectively to planet carrier ps 2  and to ring gear C 1  of first epicyclic gearset  137  and of second epicyclic gearset  138 . 
   The combination of first and second epicyclic gearsets  137  and  138  respectively constitutes a compound epicyclic gearset. 
   The power pathway formed in this way and connecting internal combustion engine  130  to wheels  133  of the vehicle constitutes the primary pathway. 
   In order to achieve continuous variation of the transmission ratio in the mode chosen between two modes of operation such as described in the foregoing, the infinitely variable transmission of the invention is provided with an electric variator composed of a first electric machine  131  and a second machine  132 . 
   As has already been described, the electric variator is also supplemented by an electrical energy storage element (not illustrated), to which there are connected the two electric machines  131  and  132 , which are electrically and mechanically reversible. 
   First electric machine  131  is connected to a reducing stage  140 , which introduces a reduction ratio K e1 , and is respectively coupled to sun gear p 2  of first epicyclic gearset  137  and to ring gear C 1  of a third epicyclic gearset  141 . 
   Third epicyclic gearset  141  is provided with a sun gear p, which is coupled to ring gear C of a fourth epicyclic gearset  142 , such that sun gear p of third epicyclic gearset  141  and ring gear C of fourth epicyclic gearset  142  are connected to the frame or to any other fixed point  145  via brake  144 ′. 
   The planet carrier of third epicyclic gearset  141  is itself coupled to such a fixed point  145  by means of a brake  144 . 
   Fourth epicyclic gearset  142  is provided with a sun gear p, which is coupled via a reducing stage  143  with gear ratio K e2  to second electric machine  132  of the electric variator of the transmission of the invention. 
   In order to control the infinitely variable transmission of the invention, the internal combustion engine, the electric variator  131 ,  132  and the two brakes  144  and  144 ′ of gearbox  134  proper are adjusted via a two-mode infinitely variable transmission controller  135 . 
   Controller  135  is provided with a controller  146  of the operating point of the motive power unit as a function of predetermined stresses. These stresses depend in particular on the condition of the environment of the vehicle, in particular its speed and the previously adjusted operating point, and on the operator&#39;s adjustment, such as the degree of depression of the accelerator pedal, or else on the adjusting signal of an automaton to adjust the vehicle speed, for example. 
   A controller  147  of the operating point of internal combustion engine  130  receives an operating point target value from controller  135  and generates adjusting signals suitable for actuators for determination of the operating point of internal combustion engine  130 . In one embodiment, such an actuator is implemented by the butterfly valve of the carburetor. 
   An operating controller  148  of first and second electric machines  131  and  132  respectively makes it possible to determine, for each machine, whether its mode of operation will be that of a motor or generator. On the basis of this determined mode of operation, the controller determines, for each machine, its speed of rotation and/or its torque or else its armature voltage and/or its armature current. In a preferred embodiment, the two reversible electric machines are electrically charged by means of an electrical energy accumulator, which cooperates with a device for management of an electrical energy accumulator. Controller  148  receives a target value of the operating point from controller  135  and produces suitable adjusting signals for the pilot-control circuits of the electric machines. Such pilot-control circuits make it possible to regulate the supply of the armature of the motor or else to orient the electrical energy produced in generator mode of operation. 
   A transmission-mode-changing controller  149  determines the open or closed state of first brake  144  and/or of second brake  144 ′ in such a way that one mode among at least two modes of operation of the infinitely variable transmission is selected by an adjusting signal of controller  135 , as described in the foregoing. 
     FIG. 4  illustrates a mechanical embodiment of the basic diagram of gearbox  134  of  FIG. 3 . This figure is substantially a half view that is symmetric relative to its axis  156  of rotation. 
   Internal combustion engine  150  is connected to a pinion  154  in such a way as to form, together with a toothing  155 , a reducing stage analogous to reducing stage  136  of  FIG. 3 . 
   Toothing  155  is mounted on a bearing that is free to rotate around a central gearbox shaft  156 . 
   Toothing  155  is integral with planet carrier  159  (PS 1 ,  FIG. 3 ) of the second epicyclic gearset  138  in  FIG. 3 , which thus constitutes the first gearset of the compound gearset of the primary power train of the invention. 
   The second epicyclic gearset  138  is provided with a sun gear  174  (P 1  in  FIG. 3 ) and with a ring gear  161  (C 1  in  FIG. 3 ). 
   First epicyclic gearset  137  in  FIG. 3  is provided with a sun gear  162  (P 2  in  FIG. 3 ), a planet carrier  160  (PS 2  in  FIG. 3 ) and a ring gear  175  (C 2  in  FIG. 3 ). 
   Planet carrier  159  of second epicyclic gearset  138  is integral with ring gear  175  of first epicyclic gearset  137 . 
   Ring gear  161  of second epicyclic gearset  138  is connected to or integral with planet carrier  160 . 
   There has therefore been achieved a compact compound gearset disposed coaxially around a central shaft of gearbox  156 . 
   In  FIG. 4 , only the upper part of this schematic view has been illustrated, in order to simplify the clarity of the description. 
   The wheels of the vehicle are coupled on a shaft  153  via pinion  158  to toothing  157 , integral with ring gear  161  of second epicyclic gearset  138 . 
   Toothing  157  is represented as a gearbox output pinion. 
   In this way, by means of the compound gearset described in the foregoing, the primary power train makes it possible to connect wheels  153  to internal combustion engine  150 . 
   There are then illustrated third and fourth epicyclic gearsets  141  and  142  respectively, which make it possible to achieve the secondary power train as well as its coupling to the variator, to the mode-changing system and to the primary power train. 
   The third epicyclic gearset  141  of the gearbox of the invention is provided with a sun gear  176  (PC in  FIG. 3 ) and a ring gear  177  (C c  in  FIG. 3 ). 
   Planet carrier  168  of third epicyclic gearset  141  is integral with brake  169  analogous to brake  144  of  FIG. 3 . 
   Fourth epicyclic gearset  142  is implemented here with a planet carrier  163 , which connects sun gear  178  to ring gear  179 . 
   To achieve power splitting and manipulations by the mode-changing system, sun gear  176  of third epicyclic gearset  141  is integral with ring gear  179  of fourth epicyclic gearset  142 . 
   Similarly, ring gear  177  of third epicyclic gearset  141  is integral with sun gear  162  of the first epicyclic gearset  137 . 
   Sun gear  176  of third epicyclic gearset  141  as well as ring gear  179  of the fourth epicyclic gearset are made integral with a first lining of a brake  170  analogous to brake  144 ′ of  FIG. 3 , the other lining of brake  170  being integral with the gearbox case. A brake actuator (not illustrated) makes it possible to activate or not activate braking by bringing the two linings together in response to an adjusting signal from the transmission&#39;s mode-of-operation controller ( 135 ,  149 ). Planet carrier  168  of the third epicyclic gearset (ps,  141 ), integral with ring gear  179  of the fourth epicyclic gearset (c,  142 ), is integral with a first lining of a brake  169 , the other lining of brake  169  being integral with the gearbox case. A brake actuator (not illustrated), associated with brake  169  of planet carrier  168 , makes it possible to activate or not activate braking thereof by bringing the two linings together in response to an adjusting signal from the transmission&#39;s mode-of-operation controller ( 135 ,  149 ). 
   Shaft of gearbox  156  is terminated at its other end relative to internal combustion engine  150  by a pinion  171 , which is connected to second electric machine  152  via a pinion  171  connected to pinion  173  via a chain  172 . 
   Pinion  173  drives the shaft of the rotor of electric machine  152 . 
   Similarly, sun gear  162  of first epicyclic gearset  137  ( FIG. 3 ) of the compound gearset carries an external toothing  165 , which is coupled via a chain  166  to a pinion  167  integral with the shaft of the rotor of first electric machine  151  of the electric variator of the infinitely variable transmission of the invention. 
   In this way there has been mechanically achieved a gearbox with which the first and second electric machines can be easily integrated externally and in which the mode-changing system is composed essentially of the two brakes  169  and  170 . 
   The two electric machines  151 ,  152  of the electric variator and the two brakes  169 ,  170  of the mode-changing system can be integrated. 
   In addition, the elements having the highest speed of rotation were disposed with high step-down ratios, thus making it possible to lower the maximum values permissible in the gearbox. 
   In  FIG. 5 , internal combustion engine  41  is able to split off the mechanical power by a first power train composed of a first epicyclic gearset  45  to which it is connected by the sun gear (access reference P). 
   Planet carrier ps of epicyclic gearset  45  is connected to wheels  43  of the vehicle via a reducing stage  53 , which applies a reduction coefficient K 0  to the speed of rotation. 
   In addition, internal combustion engine  41  can transfer mechanical power not only to driving wheels  43  of the vehicle in particular but also to first and second electric machines  42  and  44 , via a second power train, which is provided with a reducing stage  51 , which has a reduction coefficient K i  and whose output is connected to planet carrier ps of second epicyclic gearset  46 . 
   Sun gear p of second epicyclic gearset  46  is connected to the rotor of second electric machine  42 . 
   According to the invention, in this second power train there is inserted a third epicyclic gearset  47  in series with second epicyclic gearset  46  by its ring gear c, which is connected to ring gear c of second epicyclic gearset  46 . 
   In order to reassemble the two power trains, ring gear c of first epicyclic gearset  45  and sun gear p of third epicyclic gearset  47  are joined and connected also to a reducing stage  52 , which has a speed ratio K e1  and is connected to the other electric machine  44 . 
   According to the invention, the mode-changing device or system is provided essentially with a brake  48  and a clutch  49 , brake  48  is disposed between planet carrier ps of third epicyclic gearset  47  and case  50  of the infinitely variable transmission, and clutch  49  is disposed between planet carrier ps of third epicyclic gearset  47  and the point common to ring gear c of first epicyclic gearset  45  and to sun gear p of third epicyclic gearset  47 . 
   In this architecture, the infinitely variable transmission of the invention has two modes of operation, which are:
         a first mode, achieved when the brake is closed,   a second mode, achieved when the clutch is closed.       

   By virtue of the functional scheme of the present invention, matching of the infinitely variable transmission with different engines of the same power and having different maximum speeds of rotation can be achieved by matching solely the single reducing stage  51 , by choosing a suitable ratio K i . 
   When clutch  49  is closed, sun gear p and planet carrier ps of third epicyclic gearset  47  being blocked or rather joined together, gearset  47  revolves as a block. All the elements of third epicyclic gearset  47 , comprising sun gear p, ring gear c and planet carrier ps, spin at the same speed. Third epicyclic gearset  47  then does not introduce any speed-step-down ratio. 
   When brake  48  is clamped, the element of the third epicyclic gearset  47  on which it is applied, in this case the planet carrier ps, the gearset bears on case  50  and introduces a step-down ratio. 
   This arrangement also makes it possible to temporarily clamp the two couplers  48  and  49  during changes of mode. 
   In this way, it is possible to achieve a mode-changing system without interrupting the flow of torque. 
   When brake  48  is clamped, third epicyclic gearset  47  achieves a step-down ratio equal to its gear ratio, or in other words to the ratio of the number of teeth of ring gear c to the number of teeth of sun gear p. 
   In the second mode, in which clutch  49  is closed, third gearset  47  does not introduce any step-down ratio. 
   The infinitely variable transmission of the invention is provided with a controller  80  of its operation, which is connected by a bus B to a plurality of controllers or adjusting circuits of which it is composed. 
   Controller  80  is provided with a controller  81  of the operating point of the motive power unit as a function of predetermined stresses. These stresses depend in particular on the condition of the environment of the vehicle, in particular its speed and the previously adjusted operating point, and on the operator&#39;s adjustment, such as the degree of depression of the accelerator pedal, or else on the adjusting signal of an automaton to adjust the vehicle speed, for example. 
   A controller  82  of the operating point of internal combustion engine  41  receives an operating point target value from controller  81  and generates adjusting signals suitable for actuators for determination of the operating point of internal combustion engine  41 . In one embodiment, such an actuator is implemented by the butterfly valve of the carburetor. 
   An operating controller  83  of first and second electric machines  44  and  42  respectively makes it possible to determine, for each machine, whether its mode of operation will be that of a motor or generator. On the basis of this determined mode of operation, the controller determines, for each machine, its speed of rotation and/or its torque or else its armature voltage and/or its armature current. In a preferred embodiment, the two reversible electric machines are electrically charged by means of an electrical energy accumulator, which cooperates with a device for management of an electrical energy accumulator. Controller  83  receives a target value of the operating point from controller  81  and produces suitable adjusting signals for the pilot-control circuits of the electric machines. Such pilot-control circuits make it possible to regulate the supply of the armature of the motor or else to orient the electrical energy produced in generator mode of operation. 
   A transmission-mode-changing controller  84  determines the open or closed state of clutch  49  and/or of brake  48  in such a way that one mode among at least two modes of operation of the infinitely variable transmission is selected by an adjusting signal of controller  81 , as described in the foregoing. 
     FIG. 6  illustrates the kinematic diagram of an embodiment of the invention illustrated in  FIG. 5 . 
   The same elements as those of  FIG. 5  are identified with the same reference numerals. 
   The two electric machines  42  and  44  are not disposed on the same line as internal combustion engine  41 , and they can be disposed along the engine shaft, as viewed face on, with an angular offset determined by the space-requirement plans both of the IVT and of the motive power unit equipped therewith, and of the space requirement of the engine performance of the vehicle. 
   In addition, it is pointed out that it has been possible to insert third epicyclic gearset  47  between the first and second epicyclic gearsets  45  and  46  respectively of the prior art architecture without necessitating any particular lengthening of the infinitely variable transmission. 
   Output shaft  60  of internal combustion engine  41  is integral with a gear  61  engaged on a gearset composed of a gear  62  mounted on a spindle containing a gear  63 . 
   The ratio of the number of teeth of gears  61  and  62  can be matched in such a way as to produce a reducing stage equivalent to the reducing stage of the diagram of  FIG. 5  variable as a function of the speed matching in such a way as to make the infinitely variable transmission of the invention function in its optimal range at maximum speed. 
   Output shaft  60  of internal combustion engine  41  is connected at the shaft end to the sun gear of first epicyclic gearset  45 , planet carrier  68  rotates freely around engine shaft  60 , and planets  69  are engaged between ring gear  70  and the sun gear. 
   Ring gear  70  of first epicyclic gearset  45  is provided with an external toothing coupled to a pinion  72  integral with the shaft of the rotor of first electric machine  44 . 
   The reduction ratio between the number of teeth of gears  72  and  71  makes it possible to synthesize the reduction ratio K e1  of reducing stage  52  of the diagram of  FIG. 5 . 
   In addition, planet carrier  68  of first epicyclic gearset  45  is provided with an external toothing engaged on a first gear  67  axially integral with a second gear  64 , which is coupled to input pinion  65  of differential  66  connected to wheels  43 . 
   In this way there is established a reducing stage of gear ratio K 0  analogous to reducing stage  53  (see  FIG. 5 ). 
   Ring gear  70 ,  71  of first epicyclic gearset  45  is integral with sun gear  76  of third epicyclic gearset  47  via a shaft  73 , which traverses planet carrier  74  of third epicyclic gearset  47 . 
   Planet carrier  74  of third epicyclic gearset  47  has a lining, which is schematically represented at  48  and which can be activated by brake  48 . 
   Electric machine  42  has an output shaft, which is connected to sun gear  79  of second epicyclic gearset  46 , whose planet carrier  81  is engaged on ring gear  78  integral with ring gear  77  of third epicyclic gearset  47 . 
   Conversely, in the second mode of operation, the first branch is closed and the second branch is open. 
     FIG. 7  illustrates another basic diagram of an infinitely variable transmission implementing the invention. 
   Internal combustion engine  230  has an output shaft, which is connected to a first compound gearset TA implemented in gearbox  234  or belonging to the infinitely variable transmission proper. 
   First compound gearset TA is provided with a first epicyclic gearset  238 , to which internal combustion engine  230  is connected via its sun gear P 1 . 
   Planet carrier ps of first epicyclic gearset  238  of compound gearset TA is connected to a reducing stage  239  and applies a specified reduction ratio K 2 , the output being connected to driving wheels  233  of the vehicle. 
   In addition, planet carrier ps of first epicyclic gearset  238  is connected to the planet carrier of a second epicyclic gearset  237  of first compound gearset TA. 
   The ring gears of the first and second epicyclic gearsets  238  and  237  respectively are connected together, and their common movement is transmitted at a coupling over the secondary power-splitting train. 
   Sun gear P 2  of second epicyclic gearset  237  is itself connected to planet carrier ps of an epicyclic gearset TB, whose sun gear p is connected to the rotary shaft of a second electric machine  232 . 
   A first electric machine  231  is coupled via its output shaft to a reducing stage  240 , which applies a reduction ratio K E1  and is connected both to the ring gears of first and second epicyclic gearsets  238  and  237  respectively and to the ring gear of a first epicyclic gearset of a second compound gearset TC. 
   Second compound epicyclic gearset TC is also provided with a second epicyclic gearset  236  configured in such a way that the planet carriers and the sun gears of its two epicyclic gearsets  231  and  236  are coupled to one another. 
   Planet carriers PS are temporarily integral with a frame or chassis  245  by means of a first brake  244 , while the ring gear of second epicyclic gearset  236  can be made integral with the chassis or fixed point  245  by means of a second brake  244 ′. 
   The sun gears of epicyclic gearsets  231  and  236  of compound gearset TC are connected to the ring gear of epicyclic gearset TB. 
   Gearbox  234  is controlled by means of a controller  235 , which is provided essentially with a transmission calculator  246 , an internal combustion engine controller  247 , an electric variator controller  248  and a mode-changing controller  249 . 
   These various components of controller  235  are connected to different sensors of the state of operation of the vehicle as well as to sensors for detecting the operator&#39;s intent, such as a sensor for the degree of depression of the accelerator pedal. This sensor is then connected to a module for detecting the intent or wish of the operator. The link is assured by means of a bus system B. 
   Mode-change controller  249  is provided with a first output, which is transmitted to an actuator of brake  244 , and with a second output, which is coupled with an actuator of second brake  244 ′. 
   Such a mode-change controller produces, as a function of adjusting signals  246 , output signals capable of assuming four states, as follows: a first state in which both output signals are inactive, second or third states in which one or the other of the output signals is active, and a fourth state in which both output signals are active. 
   Controller  248  of the electric variator produces at least two adjusting and/or control signals destined for each of the electric machines  231  and  232  in order to determine their respective operating points according to a four-quadrant current voltage rule I. 
   Preferably the electric variator is supplemented by an electrical energy storage element (not illustrated), such as the vehicle battery or a high-value capacitor, which is managed by a charging and discharging circuit (not illustrated) under the control of controller  249 . 
   Such a mode-changing system composed of a compound gearset TC and of the two brakes  244 ,  244 ′ makes it possible to simplify the mechanical mode-changing construction without necessitating a supplementary shaft, and it facilitates installation of electric machines on gearbox  234 . 
   First and second brakes  244  and  244 ′ respectively can be disposed at the end of gearbox  234 , whereas the prior art clutches, when used to implement the mode-changing system, must necessarily be disposed at the center of this gearbox. 
   Compound gearset TA offers more possibilities for the step-down ratio and in particular a specific step-down ratio that makes it possible to reduce the speed of rotation of the elements of second compound gearset TC or splitting gearset. 
   Such an architecture permits three operating states depending on whether the brakes are open or clamped. 
   In the first mode of operation, brake  244  blocks planet carrier PS of the two epicyclic gearsets  231  and  236 . 
   Ring gear C of second epicyclic gearset  236  spins freely, and gearset TC functions as a simple gearset composed of the ring gear of first epicyclic gearset  231  of common planet carrier PS and of common sun gear P. 
   In a second state, the mode-changing system is disposed in such a way that the two brakes  244  and  244 ′ are both clamped. 
   By virtue of this fact, all elements of compound gearset TC are blocked, and it is therefore immobilized. 
   In this second mode, the two electric machines  231  and  232  are directly connected to the primary power-splitting train, and either one or the other or both can operate both as a generator and as a motor. 
   This configuration is established without blockage or mechanical interruption of the transmission during a change of mode. 
   In a third mode, first brake  244  is open and second brake  244 ′ is clamped. 
   In this configuration, ring gear C of second epicyclic gearset  236  is braked and functions as a support point. 
   In this mode, the step-down ratio is a compound ratio that is a function of the number of teeth of all the spinning elements comprising ring gear C, planet carrier PS and sun gear C of compound gearset TC. 
   In this configuration, the transmission benefits from a very broad range of achievable step-down ratios. 
   In this basic diagram, the internal combustion engine is directly connected without reduction to one of the inputs of compound gearset TA of the primary train. 
   The epicyclic gearsets are therefore all on the same line, which makes the transmission particularly suitable for motive power unit architectures with high degree of motorization. 
   In addition, the double gearset of the secondary train, composed of simple gearset TB and of compound gearset TC, makes it possible to obtain a broad range of step-down ratio. 
     FIG. 8  illustrates a mechanical layout diagram of a gearbox using the basic configuration of gearbox  234  of  FIG. 7 . 
   In this  FIG. 8 , the same elements as those of  FIG. 7  are identified with the same reference numerals and are not further described. 
   Output shaft  250  of internal combustion engine  230  is aligned with common shaft  251  of rotation of primary compound gearset TA, of compound mode-changing gearset TC and of simple gearset TB for recombination of the two splitting trains. 
   Via this shaft  250 , internal combustion engine  230  is therefore directly connected without intermediate reducing stage to sun gear PA 1  of first epicyclic gearset  238  ( FIG. 7 ). 
   Planet carrier PS A  is double and common to the two epicyclic gearsets  237 ,  238  of first compound gearset TA. Planet carrier PS A  is spinning on sun gear P A1  of epicyclic gearset  238  ( FIG. 7 ), fixed at the end of shaft  250  of internal combustion engine  230 , and it is spinning on sun gear PA 2  of second epicyclic gearset  237  ( FIG. 7 ) of compound gearset TA, fixed on a first part of shaft  251 . 
   The second part of shaft  251  carries planet carrier PS B  of simple gearset TB. 
   Common shaft  251  carries the following components, which can rotate freely and are mounted on two suitable bearings:
         ring gear CA, which is common to the two epicyclic gearsets  238 ,  237  of first compound gearset TA, and ring gear CC 1  of first epicyclic gearset  231  of second compound gearset TC;   sun gear PC of second compound gearset TC, integral with ring gear CB of simple gearset TB.       

   In this embodiment, ring gear CA of the two epicyclic gearsets  238  and  237  of the first compound gearset is provided with a single toothing to drive a single pinion of sun gear SA mounted on planet carrier PS A . Each planet gear SA of planet carrier PS A  is double, meaning that it carries:
         a first pinion engaged between sun gear PA 1  of epicyclic gearset  238  and the single toothing, in this case internal, of ring gear CA, common to the two epicyclic gearsets;   a second pinion integral with the first pinion via their common spindle and engaged on sun gear PA 2  of second epicyclic gearset  237  of first compound gearset TA.       

   Planet carrier PS A  of the first compound gearset is mounted to rotate freely on a suitable bearing disposed on output shaft  250  of internal combustion engine  230 . Planet carrier PS A  is integral with a toothed gear engaged on a pinion integral with vehicle wheels  233 . 
   In this embodiment, ring gear CA also carries an external toothing, which is engaged with a pinion  253  mounted at the end of the shaft of the rotor of first electric machine  231  of the electric variator. 
   In this embodiment, sun gear PC common to the two epicyclic gearsets  231  and  236  is provided with a single external toothing to drive a single pinion of planet gear SC mounted on planet carrier PS of second compound gearset TC. Each planet gear SC of planet carrier PS is double, meaning that it carries:
         a first pinion engaged on sun gear PC on the one hand and on an internal toothing of ring gear CC 1  of epicyclic gearset  231  ( FIG. 7 ) integral with common ring gear CA of first compound gearset TA;   a second pinion, integral with the first pinion via their common spindle and engaged on an internal toothing of ring gear CC 2  of second epicyclic gearset  236  ( FIG. 7 ) of second compound gearset TC.       

   Planet carrier PSC of the second compound gearset is mounted to rotate freely between sun gear PC of second compound gearset TC and ring gear CC 1  of its first epicyclic gearset  231  ( FIG. 7 ). 
   Shaft  251  carries planet carrier PS B  of simple gearset TB, which spins on sun gear PB, whose shaft  252 , aligned with shafts  251  and  250 , is connected to second electric machine  232 . 
   Gearsets  244  and  244 ′ have been schematically represented in the axial gap between simple gearset TB and second compound gearset TC. 
   First brake  244  is provided with a first lining integral with ring gear CC 2  of second epicyclic gearset  236  of second compound gearset TC and a second lining integral with case  245  of the gearbox. A brake actuator (not illustrated) is disposed between the two linings in such a way that, in response to the adjusting signal from transmission-mode-changing controller  249 , first brake  244  is either opened or clamped. 
   Second brake  244 ′ is provided with a first lining integral with planet carrier PSC of second compound gearset TC and a second lining integral with case  245  of the gearbox. A brake actuator (not illustrated) is disposed between the two linings in such a way that, in response to the adjusting signal from transmission-mode-changing controller  249 , second brake  244 ′ is either opened or clamped. 
   It is noted that the mode-changing system could be installed outside this space requirement in order to further narrow the axial or longitudinal extent of such a gearbox. In this case, the two brakes  244  and  244 ′ are spaced apart from central shaft  251 . 
   The mode-changing system is achieved in compact form, since compound gearset TC and braking part  244 ,  244 ′,  245  can be integrated separately.