Abstract:
A transmission between a gear ( 22 ) mounted freely to rotate about a shaft and a one-way drive-lock mechanism ( 26 ) for engaging in rotation the gear ( 22 ) and its shaft in a rotational direction, including a ring ( 52 ) integral in rotation with the shaft and bearing on its radial surface ( 54 ) at least two dogs ( 58 ) pivotally mounted about radial axes ( 62 ) between rest and locking positions on the gear ( 22 ) wherein they prevent the gear from rotation relative to the shaft. The invention is particularly applicable to transmission systems for a motor vehicle.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to transmission apparatus, in particular for a motor vehicle, of the type in which at least one pinion, mounted for free rotation on a shaft, is associated with controlled means for coupling the shaft and pinion for rotation together, the said means comprising at least one one-way locking mechanism mounted between the shaft and the pinion, together with means for actuating the said mechanism. 
     2. Description of Related Art 
     It has previously been proposed, in Applications FR 0 002 482 and FR 0 003 491 of the Applicant, to provide an automatic transmission of the gear type for a motor vehicle which comprises two clutches coupling the output shaft of an internal combustion engine with two input shafts of the transmission, driving pinions mounted on the said input shafts, driven pinions mounted on the output shaft of the transmission and in engagement with the driving pinions, and with them defining transmission ratios, one of the pinions of each ratio being coupled in rotation to its shaft while the other one is free to rotate on its shaft and is associated with control means for coupling it with the shaft, for engagement of the corresponding transmission ratio. 
     The coupling means associated with each free pinion comprise two one-way locking mechanisms which are mounted in opposite directions between the free pinion and its shaft, while actuating means of these mechanisms enable them to be selectively rendered active or inactive. 
     In one embodiment of such a transmission, the one-way locking mechanisms are arranged on the flanks of the free pinions, and comprise locking members such as catches, which are associated with return springs and with pushers for engaging on sets of teeth formed on the flanks of the free pinions, or to move away from these teeth. Cams, mounted for example inside the shaft and carrying the free pinions, are connected to an actuator through an axial rod and are able to act on the pushers so as to put the catches into engagement with the teeth on the flanks of the pinions. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the present invention is to improve transmissions of the above type so as, firstly, to enable their operation to be improved and improve their reliability, and secondly, to simplify their assembly while reducing their cost. It is also applicable to any apparatus for changing transmission ratios, whether automatic or otherwise, and whether having a simple or a double clutch. 
     To this end, it proposes transmission apparatus, in particular for a motor vehicle, comprising at least one pinion mounted for free rotation on a shaft, and controlled means for coupling the shaft and pinion for rotation together, the said means comprising two one-way locking mechanisms which are mounted between the shaft and the pinion to prevent rotation of the pinion with respect to the shaft in one direction and to permit such rotation in the other direction, and vice versa, characterised in that the said mechanisms comprise a sleeve mounted on the shaft adjacent to the pinion and coupled to the shaft for rotation therewith, at least two pallets mounted on a radial face of the sleeve for pivoting movement in opposite directions about substantially radial axes between a rest position and a locking position, means formed either on a radial face of the pinion adjacent to the said radial face of the sleeve, or on a separate attached member fixed with respect to the pinion, for abutting cooperation, in a first direction of rotation of the pinion with respect to the sleeve, with a first pallet when the latter is in its locking position, and, in the other direction of rotation of the pinion with respect to the sleeve, with a second pallet when the latter is in its locking position, first means for displacing the said first pallet between its locking and rest positions, and second means for displacing the said second pallet between its locking and rest positions, the first and second means being independent of each other and being able to displace the said first and second pallets simultaneously in their locking position. 
     Accordingly, these mechanisms are in the form of a sleeve which is mounted adjacent to the pinion on the said shaft, and which is coupled in rotation to the said shaft, for example in mating cooperation. Assembly is simple, because it is sufficient to locate the pinion and the sleeve side by side on the shaft. In addition, mounting of the pallets in radial pivoting movement makes them impervious to the effects of centrifugal force. 
     Independence of the displacement means for the first and second pallets between their rest and locking positions enables the pinion to be locked on the shaft in both directions of rotation and to be unlocked selectively in one and/or the other direction of rotation. 
     According to a further feature of the invention, an annular cover plate is fixed on the said radial face of the sleeve, and includes a window or cut-out in the region of each pallet and abutment means on a part of the pallets, these abutment means being adapted to define pivot axes for the pallets. 
     In addition, return springs, mounted between the pallets and the sleeve, constantly biases the pallet towards its locking position. 
     Where the cover plate is fixed on the sleeve, it enables the pivoting movement of the pallets to take place while preventing the latter and their return springs from escaping. The assembly of the sleeve, pallets, return springs and cover plate constitutes a module which can be assembled independently, and which has only then to be engaged on the shaft carrying the free pinion. 
     According to another feature of the invention, two members are mounted in rotation with respect to the sleeve, each said member including a finger co-operating with a pallet for displacing it from its locking position to its rest position. 
     Preferably, the said two members are rings which are axially superimposed between the sleeve and the cover plate. 
     They enable the pallets to be held in their rest position against the force exerted on the pallets by their return springs, so that the pinion is able to rotate freely on its shaft in either direction. Each ring may comprise a plurality of fingers co-operating with different pallets, which are spaced apart uniformly about the axis of rotation. 
     According to yet another feature of the invention, the said sleeve is mounted between two pinions which are free to rotate on the sleeve, and its two radial faces include said pallets for locking each of the pinions in at least one direction of rotation with respect to the shaft. 
     In another version, the sleeve includes such pallets on a single radial face, and is mounted axially between the pinion and an annular member which is fixed on the pinion and which participates in the guidance of the pinion in rotation on the shaft. 
     In one embodiment of the invention, the rings are displaced in rotation on the sleeve by radial pushers which are guided in displacement in the sleeve between a rest position and a working position, and by return springs which are mounted between the rings and engagement surfaces presented by the sleeve. 
     In particular, one pusher may be associated with each ring, to act on a lug fixed to the ring so as to cause it to rotate in one direction with respect to the sleeve, and a return spring which acts on the ring so as to rotate it in the other direction. 
     The pushers which act on the rings of the two one-way locking mechanisms of the pinion extend radially into openings in the sleeve and shaft, and means for radial displacement of the pushers are mounted within the shaft and are axially displaceable with respect to the shaft. 
     In a further version, at least one annular member external to the shaft surrounds the said sleeve and is fixed to the latter for rotation with it, the said annular member being movable axially with respect to the said sleeve and comprising ramps which cooperate with lugs radially outside the said rings, so as to displace them in rotation, means being provided for displacing the said annular member in axial translation on the said sleeve in one direction and in the other direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be understood more clearly, and further features, details and advantages of it will appear more clearly, on a reading of the description which is given by way of example and with reference to the attached drawings, in which: 
         FIG. 1  is a diagrammatic representation of an automatic gear type transmission to which the invention is applicable; 
         FIG. 2  shows diagrammatically the principle of one-way locking of a pinion, in accordance with the invention; 
         FIG. 3  is a diagrammatic exploded perspective view of a set of two one-way locking mechanisms according to the invention; 
         FIG. 4  is an exploded perspective view, shown partly cut away and representing a pinion, its one-way locking means and its rotary shaft; 
         FIG. 5  is a perspective view corresponding to  FIG. 4  but showing the pinion and its locking means mounted on the rotary shaft; 
         FIG. 6  is a perspective view of the whole of the locking means, shown on a larger scale; 
         FIG. 7  is a partial diagrammatic view in axial cross section of a modified version of the invention; 
         FIGS. 8 and 9  show diagrammatically a further modified version of the invention, with  FIG. 9  being a developed partial view of an annular member seen in FIG.  8 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference is first made to  FIG. 1 , which shows diagrammatically an automatic gear-type transmission for a motor vehicle, coupling the output shaft  10  of a heat engine M to a shaft  12  which is adapted to drive the road wheels of the vehicle in rotation through a differential. 
     The transmission comprises two input shafts  14 ,  16  which are coaxial, the shaft  16  extending within the shaft  14 , these shafts being coupled to the output shaft  10  of the engine through respective clutches E 1 , E 2 . 
     Each input shaft  14 ,  16  carries driving pinions  18 ,  20  respectively which are coupled in rotation to their shaft, and each of which is in engagement with a respective driven pinion  22 ,  24 , the meshed pairs of pinions  18 ,  22  and  20 ,  24  defining the transmission ratios numbered from first gear to sixth gear, the driving pinions of the first, third and fifth gears being on the first input shaft  14 , and those for the second, fourth and sixth gears being on the second input shaft  16 . 
     The driven pinions  22 ,  24  for the transmission ratios are free in rotation on the shaft  12 , and are in association with means for selectively coupling with that shaft. 
     For each driving pinion, these coupling means comprise two controlled one-way locking mechanisms  26 , which are mounted in opposite directions between the driven pinion and the shaft  12 , and each of which is able to occupy a rest position and a working position, one of the said mechanisms preventing a driven pinion from turning with respect to the shaft  12  in a first direction and enabling it to rotate with respect to the shaft in the opposite direction, while the other locking mechanism permits rotation of the driven pinion with respect to the shaft  12  in the first direction while preventing such rotation in the opposite direction. 
     The actuating means for the one-way locking mechanisms  26  are in this example contained within the shaft  12  and comprise two cams  28 , which are mounted on an axial rod  30  inside the shaft  12  and which are connected by means of the said rod to an actuator  32  controlled by control means of the transmission, which also control the clutches E 1  and E 2  and are connected to the control system of the engine for the purpose of exchanging information or for action. One of the cams  30  controls the one-way locking mechanisms  26  for the driven pinions of first, third and fifth gears, while the other cam  28  controls the mechanisms  26  for the driven shafts of the second, fourth and sixth gears. When a transmission ratio is engaged, the two locking mechanisms  26  of its driven pinion are in the working position, while the locking mechanisms  26  of the driven pinions of the other ratios are in the rest position. 
     To change gear, it is necessary to control two locking mechanisms of the driven pinion for the engaged gear ratio, and two locking mechanisms of the driven pinion for the new gear ratio, so as to put the first one in the rest position and the second one in the working position, and this is preferably achieved without interrupting the transmission of engine torque to the road wheels. 
     As described in the above mentioned prior Applications of the Applicant, the clutches E 1  and E 2  must be controlled in a predetermined sequence of operations in the course of which one of the driven shafts  14 ,  16  of the transmission can be temporarily braked. 
     Control of the clutches E 1  and E 2  may be obtained by means of a single actuator  34  which displaces, by means of a pivoting fork  36 , a control shaft  36  which is coaxial with the first input shaft  14  of the transmission and coupled to the latter for rotation with it. 
     The fork  36  is connected to one end of the control shaft  38  through a rolling bearing  40 , and the other end of the shaft  38  is connected to the pressure plates  42  of the clutches E 1  and E 2  through two further rolling bearings  44 ,  46  respectively. 
     The two clutches E 1  and E 2  are aligned and adjacent, and have substantially the same diameter, though they are oriented in opposite directions and their pressure plates  42  are close to each other and displaceable in opposite directions to obtain declutching. In this way, a common Belleville ring  48  may be mounted between the pressure plates so as to keep them in their gripping position when the actuator  34  is in its rest position, and so that it leaves the fork  36  and the control shaft  38  in the middle position shown in FIG.  1 . 
     When the actuator  34  displaces the upper part of the fork  36  towards the right in  FIG. 1 , the clutch E 1  is disengaged and the clutch E 2  is held engaged. Conversely, when the actuator  34  displaces the upper end of the fork  36  towards the left in  FIG. 1 , it is the clutch E 1  that is held engaged and the clutch E 2  is opened. 
     The control shaft  38 , which is coupled in rotation to the first input shaft  14  of the transmission, is not subjected to any rotational torque with respect to that shaft, and is therefore displaceable axially in translation without any difficulty, through apertures in the annular member which connects the shaft  14  to the friction discs of the clutch E 1 . 
     It will also be noted that a common brake mechanism  50  acts on the two input shafts  14  and  16  simultaneously when the rotational velocity of one of the shafts has to be reduced. It is of course the input shaft in which the clutch E 1  or E 2  is disengaged which will see its rotational velocity reduced when the brake mechanism  50  is actuated, the braking torque applied to the input shafts being very much smaller than the rotational torque provided by the engine M, and being just large enough to brake the shaft  14  or  16 , which is free to rotate. 
       FIG. 2  shows the principle of a one-way locking mechanism  26  associated with a driven pinion  22  or  24  for coupling it selectively with its shaft  12  for a given direction of rotation. 
     This mechanism  26  associated with the driven pinion, for example  22 , is coaxial with the pinion and essentially comprises a sleeve  52  which is coupled to the shaft  12  for rotation with the latter, and which carries, on its radial face  54  situated facing a corresponding radial face  56  of the pinion  22 , a pallet  58  which is mounted in a cavity  60  in the radial face  54 , and which is pivotable about a pivot pin  62  which is substantially radial with respect to the axis of rotation  64  of the sleeve  52  and pinion  22 , between a position shown in full lines in  FIG. 2 and a  position which is a locking position and which is shown in phantom lines. 
     In the latter position, the end  66  of the pallet opposite to the pivot pin  62  is in abutment on one end  68  of a cavity  70  formed in the radial face  56  of the pinion  22 . In this position of the pallet  58 , the pinion  22  is able to rotate about the axis  64  with respect to the sleeve  52  in the direction indicated by the arrow  72 , but cannot turn with respect to the sleeve  52  in the opposite direction. 
     The pallet  58  is biased constantly towards its locking position by a return spring  74  which is mounted in a blind hole  76  formed in the base of the cavity  60 , parallel to the axis of rotation  64 . 
     As can also be seen in the description that follows, the pivot pin  62  of the pallets  58  consists of one or more fingers  78  of a cover plate  80  which at least partially overlies the radial face  54  of the sleeve  52  and is fixed on this sleeve, the finger or fingers  78  of the cover plate being engaged in holes or in a radial slot  82  in the free face of the pallet  58 , at a distance from the return spring  74 . 
     A moving element  84  is guided in displacement between the radial face  54  of the sleeve  52  and the cover plate  80 , as indicated by the double arrow, so as to engage in a groove  86  in the free face of the pallet  58 , to return the latter to its rest position by compressing the spring  74  as shown in FIG.  2 . This moving element  84  is biased by a return spring towards its position of engagement on the pallet  58 , and is displaceable, in a release position of the pallet, by an actuating member such as a pusher or an external sleeve, as will be described in detail later herein. 
     The other one-way locking mechanism  26 , associated with the pinion  22  for coupling it with its shaft in the direction of rotation indicated by the arrow  72 , is formed on the same sleeve  52  by and consists of at least one further pallet  58  which is mounted the other way round from that shown in  FIG. 2 , that is to say the positions of the pivot pin and return spring of this further pallet are reversed with respect to the positions shown in  FIG. 2 , and the free end  66  of the said further pallet is able to come into abutment on the other end  68 ′ of the cavity  70  in the pinion in the locking position. 
     The two one-way locking mechanisms  26  associated with the driving pinion  22  are thus mounted on the same radial face of the sleeve  52 . 
     Each of these mechanisms can of course have a plurality of pallets  58 , spaced regularly apart about the axis of rotation  64 , and the radial face  56  of the driven pinion may have a plurality of cavities  70 , spaced apart uniformly on a common pitch circle about the axis  64 . The pallets  58  of the two one-way locking mechanisms are preferably on a common pitch circle, and the cavities  70  adapted to receive them in the locking position are also on a common pitch circle centred on the axis  64 . 
     In another version, the cavities  70  are formed in a separate attached component which is fixed to the pinion  22 . 
     One of the advantages of these mechanisms is that the displacements of the pallets  58  between their rest position and their locking position takes place parallel to the axis of rotation  64 , so that they are in consequence not sensitive to centrifugal forces. 
     Another advantage of the one-way locking mechanisms according to the invention is that they are very compact in the axial direction. 
     In addition, since the two one-way locking mechanisms of a pinion are on the same radial face  54  of the sleeve  52 , the other radial face of this sleeve can receive the two one-way locking mechanisms of a pinion which is disposed facing the said other radial face. In this way, a sleeve  52  mounted between two pinions may carry all four one-way locking mechanisms associated with these pinions, which is of great advantage in terms of axial size. 
     A further advantage of the mechanisms according to the invention is their great simplicity and ease of assembly and fitting. 
     One particular embodiment of these mechanisms and their control means will now be described with reference to  FIGS. 3  to  6 . 
       FIG. 3  shows the sleeve  52 , the radial face  54  of which has four cavities  60 , each of which is arranged to receive one pallet  58 , with two of these pallets diametrically opposed so as to constitute a one-way locking mechanism for a pinion in one direction of rotation, while the other two diametrically opposed pallets constitute the other one-way locking mechanism for the pinion in the other direction of rotation. 
     The cover plate  80 , which is arranged to overlie the radial face  54  of the sleeve  52 , has four apertures or windows  88  for the passage of the pallets  58  lodged in the said cavities  60  in the sleeve  52 . A radial edge of each window  88  includes two fingers  78  bent back at 90° inwardly and parallel to the axis of rotation, these fingers being adapted to be engaged in two corresponding cavities  82  in a pallet  58  so as to retain the pallet  58  in the corresponding cavity  60  of the sleeve  52  and, if appropriate, to define the pivot axis  62  of that pallet, though this axis may equally well be defined by other means. 
     The above mentioned moving elements which enable the pallets  58  to be put in their rest position are constituted by two flat annular rings  84  which are mounted between the radial face  54  of the sleeve  52  and the cover plate  80 . In this embodiment, the two rings  84  are superimposed axially, and are mounted within a groove  92  of corresponding form which is formed in the radial face  54  of the sleeve  52 . 
     Each ring  84  has two diametrically opposed fingers  94  which extend circumferentially and which are adapted to engage in the grooves  86  in the pallets  58  so as to put them in their rest position. 
     Each ring  84  also includes at least one lug  96  which extends obliquely outwards from the ring, and which is adapted to cooperate with a radial pusher  98  for rotating the ring  84  through a relatively small angle with respect to the axis of rotation. 
     It will be noted that the two rings  84  are symmetrical and are mounted in opposition to each other in the groove  92  in the radial face  54  of the sleeve  52 . 
     The pushers  98  for actuating the two said rings  84  extend radially, firstly in slots  100  in the inner cylindrical surface of the sleeve  52 , which are open into the above mentioned groove  92 , and secondly in radial through holes  102  in the tubular shaft  12  as can be seen in FIG.  4 . 
     The two pushers  98  are diametrically opposed and situated in a common transverse plane with respect to the axis of rotation. Two further radial pushers  98 , diametrically opposed to each other and extending at right angles to the above mentioned pushers  98 , are offset axially with respect to the latter and are arranged to actuate one-way locking mechanisms mounted on the other radial face of the sleeve  52 . 
     Preferably, the slots  100  formed in the inner cylindrical surface of the sleeve  52  have a certain axial dimension which is such as to facilitate fitting and which takes manufacturing tolerances into account, and they may be open in the radial face  54  of the sleeve as shown in the drawings. Where the sleeve  52  carries two one-way locking mechanisms, two diametrically opposed slots  100  are open in a radial face of the said sleeve, and the other two diametrically opposed slots  100  are open in the other radial face of the sleeve. 
     The pushers  98  are actuated by a cam  104  of generally cylindrical form which is displaceable axially inside the shaft  12 , and which is mounted so as to be freely rotatable on an axial tube  106 , one end of which is connected through an axial rod  30  to the actuator  32  shown diagrammatically in FIG.  1 . 
     In this embodiment, the cam  104  rotates with the shaft  12 , and the tube  106  is fixed against rotation. 
     The radially inner ends of the pushers  98  are in engagement on longitudinal ramps  108  of the cam  104 , so that the pushers  98  are displaced radially in one direction or the other when the cam  104  is displaced axially in one direction or the other within the shaft  12 . 
     Radial outward displacement of the pusher  98  causes the ring  84 , the lug  96  of which is in contact with the radially outer end of the pusher  98 , to undergo limited rotation. The direction of rotation of the ring  84  is indicated by an arrow  110  in FIG.  6 . This rotation withdraws the two fingers  94  of the ring  84  from the grooves  86  in the pallets  58 , which can then be returned to the locking position by their return springs  74 . 
     When the axial displacement of the cam  104  in the shaft  12  enables the pushers  98  to be displaced radially inwards, return means associated with the rings  84  cause the latter to rotate in the direction in which their fingers  94  are engaged in the grooves  86  of the pallets  58 , so returning the latter to their rest position. These return means consist for example of springs such as those shown at  112  in  FIG. 2 , or resiliently deformable tongues which extend in the groove  92  and are constituted for example on the annular cover plate  80 . 
     The operation of the locking mechanism corresponds to that already described in the above mentioned prior art patent applications of the Applicant. Each of the two locking mechanisms associated with a pinion is actuated by one pusher  98 . When the two pushers are in a radially inner position, the two locking mechanisms are out of use and the pinion is free to rotate on the shaft  12 . When one of the pushers  98  is displaced radially outwards by the cam  104 , the corresponding locking mechanism is brought into use and the pinion is able to rotate with respect to the shaft  12  in only one direction of rotation. When both pushers  98  have been displaced radially outwards by the cam  104 , both locking mechanisms are in use and the pinion is coupled in rotation with the shaft  12 . 
     The sleeve  52  carrying the locking mechanisms is mounted so as to be rotatable with the sleeve  12 , by any appropriate means. For example, longitudinal splines are formed on the inner cylindrical face of the sleeve  52  and cooperate with corresponding longitudinal splines formed on the shaft  12 . 
     The axial position of the sleeve  52  on the shaft  12  is preferably determined by a shoulder on the outer cylindrical surface of that shaft. 
     The axial clearance between the pinion  22  and the sleeve  52  is small (typically a few tens of millimetres). 
     Fitting and assembly of the one-way locking mechanisms according to the invention is extremely simple: 
     The pallets  58  are first positioned in the cavities  60  in the sleeve, their return springs  74  being introduced into the holes  76 , and the rings  84  are then put in place and the annular cover plate  80  is positioned on the corresponding face of the sleeve  52  and fixed to the latter by any appropriate means, for example by seaming or the like. 
     For fitting them on the shaft  12 , the pinions  22 ,  24  and the sleeves  52  are threaded alternately on the shaft  12 , the pushers  98  being entirely within the shaft  12  as shown in FIG.  4 . 
     The cam  104  is then displaced within the shaft  12 . The frusto-conical end of the cam  104  displaces the pushers  98  radially outwards, after which the latter descend once again on the ramps  108 . It will be noted that the pushers  98  in radial engagement on the ramps  108  of the cam  104  enable the cam  104  to be coupled in rotation with the shaft  12 . 
     In another version, and as shown in  FIG. 7 , each sleeve  52  includes two one-way locking mechanisms working in opposite directions on only one of the radial faces, and is associated with a single driven pinion  22  or  24 . In this case, the sleeve  52  is mounted between the pinion  22  or  24  and an annular member  114 , which has an axial flange  116  for fastening it to the pinion and which plays a part in guiding the rotation of the latter on the shaft  12 . Spacing sleeves  118  are mounted on the shaft  12  between the sleeves  52 , and support the driven pinions  22  or  24  and the members  114 . 
     In another embodiment which is shown in  FIGS. 8 and 9 , the actuating means of the one-way locking mechanisms are not mounted within the shaft  12  but are arranged around the said sleeves  52 . In the example in  FIGS. 8 and 9 , each sleeve  52  mounted on the shaft  12  between two driven pinions  22  or  24  carries two one-way locking mechanisms on each of its radial faces, and is surrounded by two annular members  120  which are arranged to control the locking mechanisms, each annular member being coupled to the sleeve  52  for rotation with the latter and being displaceable axially in translation on the latter, for example by means of a fork (not shown) engaged in a peripheral groove or slot  122  in the corresponding annular member  120 . 
     The one-way locking mechanisms have a structure similar to that shown in  FIG. 3 , but the rings  84  are formed, in place of the lugs  96  co-operating with the pushers  98 , with lugs which are oriented radially outwards and which are designated by the references  124  in  FIG. 9  (which is a partial developed view of an annular member  120 ), and the ends of which are guided in grooves  126  formed in the inner cylindrical surfaces of the annular members  120 , these grooves being oriented generally partly parallel to the axis of rotation  64 . 
     As shown in  FIG. 9 , an additional groove  128  parallel to the axis may be formed in the inner cylindrical surface of each annular member  120 , for the purpose of receiving a projecting element formed on a corresponding surface of the sleeve  52 , which enables the member  120  and sleeve  52  to be coupled together in rotation while enabling the member  120  to be displaced axially around the sleeve  52 . 
     Each groove  126  receiving the end of a radial lug  124  of a sleeve  84  comprises two portions  130  parallel to the axis and joined together by a portion  132  which is oblique with respect to the axis, the oblique portions  132  of the two grooves  126  being offset axially with respect to each other. 
     Under these conditions, when an annular member  120  is displaced by axial translation on the sleeve  52  between the three positions indicated at  0 ,  1  and  2  in  FIG. 9 , the rings  84  are displaced in rotation about the axis  64  in the following way: 
     when the sleeve  52  passes in relation to the members  120  from position  0  to position  1 , a first lug  124  (the topmost one in  FIG. 9 ) is displaced angularly about the axis of rotation, while the other lug  124  keeps its angular position; 
     when the sleeve  52  is displaced in relation to the annular member  120  from position  1  to position  2 , the lug  124  of the first ring  84  keeps its angular position while the lug  124  of the other ring  84  is displaced angularly about the axis  64 . 
     Thus, when the annular member  122  is displaced between positions  0  and  2 , the two one-way locking mechanisms associated with a driven pinion change state, the pinion being free to rotate on the shaft  12  if it was previously coupled in rotation to that shaft and vice versa. 
     The two annular members  120  may be displaceable axially on the sleeve  52  by translation through two steps in the same direction between position  0  and position  2  and vice versa, or, alternatively, the two members  120  may be displaceable in one step on either side from the middle position  1 .