Abstract:
An infinitely-variable transmission with double mode power transmission for a motor vehicle, provided with a combustion engine, including a first power transmission path with a composite epicyclic gear train connecting the combustion engine to the vehicle wheels, a second power transmission path with a simple epicyclic gear train, two electric motors providing a continuous speed variator, a second simple epicyclic gear train for mode change, and an engagement/disengagement unit that can block or release a mode-changing body in the second epicyclic gear train, according to the operating mode. The engagement/disengagement body includes a sliding sleeve with a dog tooth, which can be displaced by a hydraulic actuator and with two sets of dog teeth fixed to a mode-changing body in the second epicyclic gear train.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to an infinitely variable transmission with two-mode power branching, for a motor vehicle equipped with a combustion engine. 
   FIELD OF THE INVENTION 
   With this kind of power branching transmission it is possible to obtain continuous variation from a reverse ratio to a forward ratio, passing through a special position called the “neutral engaged” position, in which the speed of the vehicle is zero, at any speed of the combustion engine. 
   DESCRIPTION OF RELATED ART 
   Power branching transmissions are of several types. 
   In a first type known as “input coupled”, the transmission includes a pair of power branching pinions which take power from the input of the mechanism and a “combining” epicyclic gear train which combines the powers at the output of the mechanism. The transmission also includes a speed controller. 
   In another type, called “output coupled”, the transmission includes a power-dividing epicyclic gear train at the input of the mechanism and a pair of power-combining pinions at the output of the mechanism. The transmission also includes a speed controller. 
   Finally, there are also known power-branching transmissions called “two matching point” transmissions, in which a first power-dividing epicyclic gear train is placed at the input of the transmission, while a second power-combining epicyclic gear train is fitted at the output of the transmission. 
   In this case also, the transmission includes a speed controller. 
   An infinitely variable transmission (IVT) uses only one or two of these three operating principles. 
   Clearly, it is useful to have two operating modes available for a single transmission, since this makes it possible to increase the range of transmission ratios and also makes it possible to decrease the dimensions of the speed controller device which can comprise electrical machines. 
   However, such two-mode transmission architectures, of the known type, have the disadvantage that the mode changes are carried out by multi-disk clutches positioned at the output of the transmission, in such a way that their operation is accompanied by abrupt changes of torque which cause disagreeable sensations for the users. Another disadvantage of such a transmission, described for example in U.S. Pat. No. 5,558,589 and U.S. Pat. No. 5,935,035, consists in the complexity of the architecture, due in particular to the presence of at least two clutches and one brake. 
   In a preceding French patent application FR 02 14 241 in the name of the present applicant, there is a description of an infinitely variable transmission with two operating modes, of the type having an electrical speed controller and at least two power branching paths, of which a main path links the combustion engine to the driving wheels, and a secondary path is connected to the electrical speed controller, in such a way that at least two operating modes can be used in the power branching path of the electrical speed controller. 
   The infinitely variable transmission described in this prior patent application comprises a first compound epicyclic gear train which enables the combustion engine to be linked to the wheels of the vehicle along a main power branching path and a simple epicyclic gear train which enables the power branching to be carried out, together with a second compound epicyclic gear train, thus forming a system for changing modes between at least two operating modes of the infinitely variable transmission. 
   The transmission described in this prior patent application comprises two engagement/disengagement devices which enable two shafts of the transmission to be independently locked or released with respect to rotation, thus providing one of the operating modes of the transmission on each occasion. 
   When there is a change of mode, the two engagement/disengagement devices are driven independently by two actuators which can be moved by an electrical force or a hydraulic force. The two actuators are operated in such a way that the two modes are engaged simultaneously, the aforesaid two shafts of the transmission being simultaneously locked with respect to rotation. 
   In a practical embodiment of this transmission, the mode change operation is carried out by means of multi-disk hydraulic brakes. This requires a relatively complex hydraulic circuit to provide a suitable supply to the two hydraulic brakes whose bulkiness is an additional drawback. Moreover, the energy consumption required for actuating the linings of the brakes used and for keeping them in the locked position causes a decrease in the efficiency of the transmission. The same applies to the frictional torque of the brakes in the open position. 
   Finally, if the hydraulic supply circuit fails, the two brakes are automatically set to the open position. In this case, the transmission is said to be “open” and certain operations, such as the starting of the combustion engine of the vehicle, by one of the two electrical machines, cannot be carried out. 
   SUMMARY OF THE INVENTION 
   The present invention relates to an infinitely variable transmission using two distinct operating modes and including a mode changing device for changing from a first operating mode to a second operating mode. 
   The object of the present invention is an infinitely variable transmission with two operating modes which overcomes these drawbacks. 
   Another object of the present invention is a transmission of this kind in which the efficiency of the transmission is improved. 
   Another object of the present invention is a transmission of this kind in which each operating mode is kept stable even if there is a failure of the supply to the means of driving the mode change device. 
   Another object of the present invention is to simplify the transmission architecture so as to reduce its overall dimensions and its production cost. 
   Another object of the present invention is an infinitely variable transmission with two operating modes in which the switch between the two operating modes is carried out in a particularly simple way. 
   The infinitely variable transmission with power branching and two operating modes according to the invention, for a motor vehicle equipped with a combustion engine, is of the type comprising a first main power branching path with a compound epicyclic gear train linking the combustion engine to the wheels of the vehicle, a second power branching path with a first simple epicyclic gear train, two electrical machines forming a continuous speed controller and a second simple epicyclic gear train for mode changing, together with an engagement/disengagement unit capable of locking or releasing a member of the second epicyclic gear train for mode changing, according to the operating mode. 
   The engagement/disengagement unit comprises a sliding sleeve provided with dog toothing which can be displaced by a hydraulic actuator and two sets of dog teeth, each fixed to a member of the second epicyclic gear train for mode changing. 
   The control of such a sliding sleeve is particularly easy to implement, and this simplifies the construction of the transmission. Moreover, the efficiency of the transmission is improved, since the power is transmitted by the dog teeth without any risk of relative slipping and without the need to apply a permanent force to the brake disks. 
   The hydraulic actuator can comprise a piston and two hydraulic feed chambers located one on each side of the active part of the piston. 
   The piston can be connected to the sliding sleeve, for example, by means of a spring washer. 
   In an advantageous embodiment, the hydraulic actuator is located axially on only one side of the sliding sleeve, making the structure more compact. 
   As a general rule, the sliding sleeve can occupy two positions, in each of which the dog toothing of the sliding sleeve engages with only one set of dog teeth of a member of the second epicyclic gear train for mode changing. Thus the transmission is in one or other of its modes, according to the position of the sliding sleeve. 
   Preferably, in a first position of the sliding sleeve, the dog toothing of the sliding sleeve is in engagement with the toothing of the sun gear of the second epicyclic gear train for mode changing, and in a second position the sliding sleeve dog toothing is in engagement with the planet carrier of the second epicyclic gear train for mode changing. 
   In all cases, the dog toothing of the sliding sleeve is such that it is in engagement with the two sets of dog teeth each of which is fixed to the members of the mode changing gear train during the change between its two positions. For example, it is acceptable for the axial length of the dog toothing of the sliding sleeve to be chosen so that it enters into engagement with one set of teeth while it is still in engagement with the other set of teeth. Thus the two members of the mode changing gear train are fixed with respect to rotation by the sliding sleeve during mode changes. 
   A retaining device with balls and springs can interact with the sliding sleeve to retain it in position in each of its two positions. 
   Thus, in all cases, the sliding sleeve remains in position, with an engaged mode, if, for example, the oil supply to the hydraulic actuator is defective or insufficient; this creates a safety factor for the use of the transmission. 
   The hydraulic feed chambers can be sealed by joints of different types, for example sealing rings or lip seals. 

   
     BRIEF DESCRIPTION OF THE DRAWING(S) 
     The invention will be more clearly understood from a study of a specific embodiment provided by way of example and without any restrictive intent and illustrated by the attached drawings, in which: 
       FIG. 1  shows schematically the main functional elements of an infinitely variable transmission according to the invention; 
       FIG. 2  shows schematically a practical embodiment of this transmission; and 
       FIG. 3  shows, in partial section, an example of practical embodiment of the mode changing control device. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   As shown in the functional diagram of  FIG. 1 , the infinitely variable transmission is fitted between a combustion engine  1  which constitutes a power unit of a motor vehicle and the axle  2  of the driving wheels of the vehicle which constitutes the driven element. The transmission comprises a first main power branching path with a compound epicyclic gear train  3   a ,  3   b . The ring gear Ca of the gear train  3   a  is fixed to the planet carrier PSb of the gear train  3   b . Similarly, the ring gear Cb of the gear train  3   b  is fixed to the planet carrier PSa of the gear train  3   a.    
   A second power branching path comprises a first simple epicyclic gear train indicated by  4 . Two electrical machines, indicated by  5  and  6  respectively, constitute a continuous speed controller. Finally, a second simple epicyclic gear train indicated by  7 , acting as a mode changing device, is associated with an engagement/disengagement unit  8  and completes the essential structure of the transmission. 
   The power supplied on the output shaft  9  of the combustion engine  1  passes through a reduction unit  10  and is supplied directly to the input  11  of the compound gear train  3   a ,  3   b . At the output  20  of the transmission, the power passes through a reduction unit  21  before being directed to the wheels  2 . 
   The first electrical machine  5  transmits power via its output shaft  12  through a reduction unit  13  which is connected, on the one hand, to the sun gear P a  of the first gear train  3   a  and, on the other hand, to the ring gear C 7  of the mode changing gear train  7 . 
   The second electrical machine  6  transmits power via its output shaft  14  through a reduction unit  15  connected directly to the sun gear P 4  of the gear train  4 . The planet carrier PS 4  of this simple gear train  4  is fixed to the sun gear P b  of the gear train  3   b . The ring gear of the simple gear train  4  is fixed to the sun gear P 7  of the mode changing gear train  7 . 
   The engagement/disengagement unit  8  comprises two dog tooth systems  16 ,  17 . The dog tooth system  16  can immobilize the planet carrier PS 7  of the mode changing gear train  7 . The dog tooth  17  can immobilize the sun gear P 7  of the mode changing gear train  7 , thus also immobilizing the ring gear C 4  of the gear train  4  to which it is fixed. 
   In  FIG. 2 , where identical elements have the same references, the engine  1  is connected, by means of a damper device  18 , to a set of reduction gears  10  which transmits the power to the input point  11  which is connected to the planet carrier PSb and also to the ring gear C a . The electrical machine  5  transmits its power via the reduction unit  13  to the sun gear Pa of the epicyclic gear train  3   a  and to the ring gear C 7  of the epicyclic gear train  7  for mode changing. 
   The electrical machine  6  transmits its power via the reduction unit  15  through the central shaft  19  to the sun gear P 4  of the epicyclic gear train  4 . Finally, the output  20  of the transmission receives power through the common point between the ring gear C b  of the epicyclic gear train  3   b  and the planet carrier PSa of the epicyclic gear train  3   a . This output is connected by the reduction gears  21  to a differential  22 , and then to the vehicle wheels  2 . 
   The sun gear P 7  of the mode changing gear train  7  is fixed to an annular member  23  which carries a set of dog teeth  24  on its periphery. Similarly, the planet carrier PS 7  of the mode changing gear train  7  is fixed to an annular member  25  which carries a set of dog teeth  26  on its periphery. A sliding sleeve  27  can move axially parallel to the axis of the transmission. The sliding sleeve  27  has a set of dog teeth  28  and also has cavities  29  and  30  which can interact alternatively with retaining balls  31  subject to the action of springs  32 . 
     FIG. 3  shows, by way of example, a possible practical embodiment of this structure. 
   Similar members are given the same references.  FIG. 3 , which is a partial section through a transmission, essentially shows the mode changing epicyclic gear train, indicated by  7  in  FIG. 2 , the other elements of the transmission being omitted to simplify the figure.  FIG. 3  shows the planet carrier PS 7  of the mode changing gear train  7 , of which one shaft  33  and a planet gear  34  are visible. The annular member  25  is fixed to the planet carrier PS 7  by a fixing element  35 . 
     FIG. 3  also shows the sun gear P 7  of the mode changing gear train  7  whose toothing  36  engages with the planet gears such as the gear  34 . The annular member  23  is fixed to the sun gear P 7  by means of a fixing ring  37 . 
   The sliding sleeve  27  is movable axially with respect to the fixed frame  38  of the transmission by means of an annular support piece  39  which has one or more housings  40  for springs  32  acting on retaining balls  31 , the whole assembly forming a ball-type retaining device. In the section shown in  FIG. 3 , only one ball  31  is visible. Transverse ribs  41 , formed respectively on the outer periphery of the sliding sleeve  27  and inside the bore of the fixing ring  39 , enable the sliding sleeve  27  to slide axially and to be fixed with respect to rotation. 
   The sliding movement of the sliding sleeve  27  is provided by a double-acting hydraulic actuator  42 , consisting of a movable piston  43  moving with respect to a set of fixed walls which is fixed to the frame  38  and which acts as a cylinder. These fixed walls comprise, in particular, an outer wall  44  forming a first outer ring gear, an intermediate wall  45  forming a second intermediate ring gear, and an inner wall  46  formed on an intermediate piece fixed to the frame  38 . The piston  43  itself has an outer ring gear  47  and an inner ring gear  48 , which are interconnected by a radial flange  49 . The piston  43  is connected mechanically to the sliding sleeve  27  by a spring washer  50 . Finally, the assembly is completed by a radial flange  51  which provides the external guiding of the piston  43 . 
   The piston  43  is moved by a hydraulic pressure which can be exerted in two hydraulic feed chambers  52  and  53 . It will be noted that the hydraulic chamber  52  is formed between the annular wall  44  fixed to the frame  38  and the annular ring gear  47  of the piston  43 , and is sealed by the piston  43 . The hydraulic chamber  53  is formed between the internal bore of the intermediate wall  45  fixed to the frame  38  and the outer cylindrical face of the inner annular ring gear  48  of the piston  43 . Thus the two hydraulic operating chambers  52 ,  53  are formed as a thin annular space between two facing annular walls. The chamber  53 , which is radially further inward, can move the piston  43  from the left towards the right of  FIG. 3  when the pressure of the hydraulic fluid in the chamber is raised; in other words, it can cause a movement of the sliding sleeve  27  out of the position which it occupies in  FIG. 3 , against the retaining force exerted by the balls  31 . The piston  43  is moved in the opposite direction, in other words from the right to the left of  FIG. 3 , by feeding pressurized hydraulic fluid into the other feed chamber  52  located radially farther outward. 
   The feed chambers  52 ,  53  are sealed, in the illustrated example, by sealing rings indicated by  54  and  55  for the chamber  52 , and indicated by  56 ,  57  and  58  for the chamber  53 . 
   Clearly, the sealing rings can be replaced with overmoulded lip seals or four-lobed seals which, although more expensive, can provide better sealing and less friction. 
   It will be noted that the piston  43  is mounted in the frame  38  so as to be entirely located on one side of the sliding sleeve  27 , which, by comparison with the ordinary operating structures of brakes or hydraulic clutches, considerably simplifies the architecture of the transmission and enables a more compact assembly to be achieved. 
   The change from one operating mode of the transmission to another is made in a reversible way by a simple change of feed to the chambers  52  and  53  by pressure pipes not shown in the figure. 
   In the idle state, the dog toothing  28  of the sliding sleeve  27  is engaged with the toothing  24  fixed to the sun gear P 7  of the mode changing gear train  7 . This position is shown in  FIG. 3 . When fed to the chamber  53 , the pressurized oil exerts an axial thrust on the piston  43  which moves from the left to the right in  FIG. 3 , and by this movement drives the sliding sleeve  27  against the retaining force of the balls  31 . During this change from one operating mode to the other operating mode, the dog toothing  28  of the sliding sleeve  27  passes through a state in which it engages simultaneously with the toothing  24  fixed to the sun gear P 7  and with the toothing  26  fixed to the planet carrier PS 7 . In this state, the two modes are therefore engaged simultaneously, the sun gear P 7  and the planet carrier PS 7  being simultaneously immobilized with respect to rotation by the sliding sleeve  27 . 
   As the feed to the chamber  53  continues, the piston  43  continues to move and maintains its thrust on the sliding sleeve  27  until the latter occupies the position in which the balls  31  enter the housings  29 . In this position, the dog toothing  28  of the sliding sleeve  27  engages exclusively with the toothing  26  which is fixed to the planet carrier PS 7 , which puts the transmission in its second operating mode. 
   It will be noted that, in both operating modes, the sliding sleeve  27  is kept in a stable state by the balls  31  which are driven by their springs  32  and are housed alternately in the housings  29  or  30 . 
   Consequently, a failure in the hydraulic feed has no effect on the state of the transmission, which remains in the engaged mode. 
   Moreover, the efficiency of the power transmission is improved because of the presence of the dog toothing which transmits the power by a mechanical positive coupling and not by friction, as is the case when brakes or hydraulic clutches are used. 
   The change of mode which is the converse of the above is carried out by feeding the hydraulic chamber  52  which returns the piston  43  to the position shown in  FIG. 3 . 
   It will be noted that the arrangement of the piston  43  and the operating chambers  52 ,  53  is such that the volume of said chambers is as small as possible, in order to minimize the filling volume and consequently the duration of the movement of the sliding sleeve  27  and the clutching time.