Abstract:
A shift element comprising at least three shift positions for shifting two gear transmission ratios in which in a first end position, which corresponds to a first shift position, the first gear transmission ratio is engaged and in a second end position, which corresponds to a second shift position, the second gear transmission ratio is engaged, while in the central position, which corresponds to a third shift position, both gear transmission ratios are engaged.

Description:
[0001]    This application is a National Stage completion of PCT/EP2008/059859 filed Jul. 28, 2008, which claims priority from German patent application serial no. 10 2007 040 040.5 filed Aug. 24, 2007. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a shift element with at least three shift positions for shifting two transmission gear ratios. 
       BACKGROUND OF THE INVENTION 
       [0003]    In manual shift transmissions, automated manual shift transmissions and dual-clutch transmissions, according to the prior art gears are engaged or preselected by means of conventional claw elements or synchronizers. In such cases, when two gear transmission ratios are adjacent and on one shaft, depending on the position of the shift actuation element one or the other of these two adjacent transmission ratios can be engaged or coupled to the shaft, or in the neutral position of the shift actuation element both gear transmission ratios can be disengaged. 
         [0004]    In some transmission designs, for example dual-clutch transmissions, owing to the arrangement of the transmission ratios it is necessary, when the shift actuation element is in a neutral position, for the two adjacent gear transmission ratios on one shaft both to be shifted to be able to preselect a gear, because of the design. For such transmission designs conventional synchronizers and claw-type shift elements cannot be used, since with such elements the shifting sleeve can always engage only one gear and in the neutral position both gears are disengaged. Below, examples of such transmission designs are described briefly. 
         [0005]    For example, a transmission of the type is known from DE 10232831 A1 by the present applicant. The known dual-clutch transmission, which has a countershaft structure, comprises a driveshaft which can be coupled, via a first clutch, to a shaft of a first part-transmission and, via a second clutch, to a shaft of a second part-transmission, the part-transmissions respectively providing different transmission ratios by means of auxiliary transmissions which can be activated by synchronizers. In this case, for synchronization of a shift element of the respective first auxiliary transmission the corresponding clutch of each part-transmission can be actuated appropriately; in addition, for each part-transmission at least one synchronization clutch is provided. 
         [0006]    From DE 10232835 A1 by the present applicant a dual-clutch transmission for a motor vehicle is known, which comprises at least two transmission groups with shafts, shift elements and gearwheels, such that the transmission groups can be connected in the force flow to a common driveshaft by means of shift-under-load clutches associated with the transmission groups. In this known transmission each transmission group is so configured that it comprises at least two main branches, and the main branches of each transmission group have gearsets downstream from them via which, by means of shift elements, a connection can be formed to a common output gearwheel of a drive output shaft. 
         [0007]    Furthermore, from DE 3233931 C2 a power take-off for a transmission with an incorporated dual clutch is known, such that the power take-off comprises a first transmission mechanism connected or locked to the main take-off shaft and a second transmission mechanism locked or connected to the main running shaft as well as a clutch device, which works in such manner that the transmission mechanisms can be selectively coupled in driving connection with the take-off transmission shaft. 
       SUMMARY OF THE INVENTION 
       [0008]    The purpose of the present invention is to provide a shift element with at least three shift positions for shifting two transmission gear ratios, in which, in a first end-position corresponding to a first shift position the first transmission gear ratio is shifted and in a second end-position corresponding to a second shift position the second transmission ratio is shifted, by the use of which two adjacent transmission gear ratios on one shaft can be shifted at the same time. The shift element according to the invention should in particular be suitable for dual-clutch transmissions, dual-clutch transmissions of group configuration and planetary transmissions, and should be able to be combined with both synchronizers and claw-type shift elements. In addition, its structure should be compact. 
         [0009]    According to the claims a shift element is proposed, which has at least three shift positions for shifting two transmission gear ratios, with which, in a first-end position corresponding to a first shift position the first transmission ratio is engaged and in a second end-position corresponding to a second shift position the second transmission ratio is engaged, while in the central position corresponding to a third shift position both transmission ratios are engaged. 
         [0010]    In a first embodiment of the invention a shift element derived from a conventional synchronizer device or from a conventional claw-type shift element with no synchronizer device is proposed, in which the axial length of the shifting sleeve is modified in such manner that in the neutral position of the shifting sleeve its inner claw teeth engage simultaneously in the outer claw teeth of the clutch elements of both transmission gear ratios. 
         [0011]    With a shift element of such design, when one gear is disengaged and at the same time another gear is engaged, displacement of the shifting sleeve into the torque-loaded claw teeth is necessary, but this requires high actuator forces. 
         [0012]    In a second embodiment of the invention a shift element derived from a conventional synchronizer device or from a conventional claw-type shift element with no synchronizer device is proposed, which comprises a shifting sleeve divided into two halves or parts so that only half or part of the shifting sleeve has to be moved, by which the associated gear is to be disengaged or engaged. The other shifting sleeve half of the engaged and thus torque-delivering gear remains untouched. 
         [0013]    According to the invention, the shift actuator has three positions in the conventional manner, such that the movement of the two shifting sleeve halves is independent so that depending on the position and movement direction of the shift actuator either one or the other shifting sleeve half is moved. The gear associated with the respective shifting sleeve half is disengaged by a positively locking carrier element on the receptor of the shift actuator, so that decoupling and coupling of the shifting sleeve halves during the shifting or engagement and synchronization of a gear take place in the shift actuator receptor. 
         [0014]    Advantageously, conventional claw teeth can be used on synchronizer elements (if provided), clutch elements, synchronizer rings (if provided) and sliding sleeve halves. 
         [0015]    By virtue of the design concept according to the invention a compact shift element is obtained, which fulfills the above-mentioned requirements regarding the simultaneous shifting of two gears and the alternate disengagement and re-engagement of a respective gear. In that the claw teeth of the components can be adopted as they exist, only the design of the sliding sleeve and its connection to the shift actuator receptor are modified. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Below, an example of the invention is explained in more detail with reference to the attached figures, which show: 
           [0017]      FIG. 1 : Schematic sectioned view of a shift element designed in accordance with a first embodiment of the invention; 
           [0018]      FIGS. 2 and 2A : Schematic sectioned views of a shift element designed in accordance with a second embodiment of the invention, in the central position with a disengaged gear; 
           [0019]      FIGS. 3-3C : Four schematic sectioned views of a shift element according to a third embodiment of the invention, to illustrate the individual shift operations; 
           [0020]      FIG. 4 : Schematic view of a further embodiment of the invention; 
           [0021]      FIG. 5 : Schematic view of a further embodiment of the invention; 
           [0022]      FIG. 6 : Schematic view of another design of a shift element according to the invention; 
           [0023]      FIG. 7 : Schematic view of another design of a shift element according to the invention; 
           [0024]      FIGS. 8-8B : Schematic views of the shift element according to the invention shown in  FIG. 7 , to illustrate the re-engagement and synchronization of the disengaged gear by overlapping rotation movements; 
           [0025]      FIGS. 9 and 9A : Schematic views of another design of a shift element according to the invention; 
           [0026]      FIGS. 10 and 10A : Schematic views of a further, advantageous design of a shift element according to the invention; 
           [0027]      FIGS. 11-11B : Schematic views of another advantageous design of a shift element according to the invention, to illustrate the re-engagement and synchronization of the disengaged gear by the driven motion of adjusting blocks; 
           [0028]      FIGS. 12-12C : Schematic views of an alternative embodiment of the shift element shown in  FIG. 11 , to illustrate the re-engagement and synchronization of the disengaged gear; and 
           [0029]      FIG. 13 : An overview of the functionality of a conventional synchronizer and the synchronizer concept proposed according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    The description below is given with reference to shift elements derived from conventional synchronizer devices; as already explained, however, it is also possible to derive the shift element according to the invention from a conventional claw-type shift element with no synchronizer device, and in that case the functions of the synchronizer element that are relevant for the invention are assumed by a part of the claw shift element arranged fixed on a shaft. 
         [0031]    In a first embodiment of the invention as shown in  FIG. 1 , the shift element  1  is in the form of a conventional synchronizer device comprising clutch elements  2 , synchronizing rings  3  and a synchronizer element  4 , in which the axial length of the shifting sleeve  5  is modified such that in the central position of the shifting sleeve  5  its inner claw teeth engage simultaneously in the outer claw teeth of the clutch elements  2  of both adjacent transmission gear ratios or gearwheels  6 ,  7  arranged on one shaft. In contrast to a conventional synchronizer, in the central position of the shift element according to the invention both gears are engaged, as can also been seen in  FIG. 13  in which the shift element in  FIG. 1  is denoted as alternative  1 . 
         [0032]    In the embodiment shown in  FIGS. 2 and 2A  the shifting sleeve of the shift element  1  is divided and so has two shifting sleeve halves  8 ,  9 . In the figure the shift actuator receptor  10 , which forms the connecting member of the shift element  1  to the shift actuator and comprises a positively locking carrier element  11  for the shifting sleeve halves  8 ,  9 , is represented schematically. The shift actuator receptor  10  is designed with a  11  shape and has a carrier  14  positioned centrally, so that the sides form the carrier elements  11 . 
         [0033]    According to the invention, axially acting spring elements  12 ,  13  are positioned on the inside of the shift actuator receptor  10  between the central carrier  14  of the shift actuator receptor  10  and the inside end faces of the two shifting sleeve halves  8 ,  9 . When, now, the left-hand gear is disengaged, the shift actuator receptor  10  is moved to the right, although it takes the left shifting sleeve half  9  with it by means of the carrier element  11 , but the right shifting sleeve half  8  is not moved since, to accommodate the movement of the shift actuator receptor  10 , the spring  12  on the right is compressed. During this the spring force on the shifting sleeve half  8  can be supported against a retaining ring or on the gearwheel. According to the invention, the spring elements  12 ,  13  are designed such that the spring force is at least as large as the force required to synchronize and engage the claw teeth. 
         [0034]    In  FIG. 2A  the shift actuator is in its central position so that both gears are engaged. Thus, the inner claw teeth of the two shifting sleeve halves  8 ,  9  engage both in the claw teeth on the synchronizer element  4  and in the claw teeth on each of the clutch elements. 
         [0035]    The mode of operation of the shift element shown will be explained below, considering the example of “disengaging the gear on the left and re-engaging it”. Starting from the neutral position, to disengage the gear on the left the shift actuator is moved to the right so that the carrier element  11  of the shift actuator receptor  10  carries with it the shifting sleeve half  9  on the left to be shifted and pushes it to the right, so that the claw teeth of the left-hand clutch element are now no longer engaged with the inner claw teeth of the left shifting sleeve half  9  as illustrated in  FIG. 2 . As can be seen in the figure, the position of the right shifting sleeve half  8  remains unchanged (i.e. the right-hand gear remains engaged) because of the compression of the spring  12 . 
         [0036]    To re-engage the gear on the left, the shift actuator receptor  10  is now moved to the left again, i.e. back to its central position. During this the left shifting sleeve half  9  is pushed to the left by the force of the left spring  13 . 
         [0037]    In contrast to a conventional synchronizer, in the central position of the shift element according to the invention both gears are engaged, as also illustrated in  FIG. 13  in which the shift element shown in  FIGS. 2 and 2A  is denoted as alternative  1 . 
         [0038]      FIGS. 3 ,  3 A,  3 B and  3 C show a further embodiment of a shift element according to the invention, in which the shifting sleeve is also divided into two shifting sleeve halves  8 ,  9 . In this design as well the shifting sleeve halves  8 ,  9  are moved by a carrier element  11  of the shift actuator receptor  10 , but to prevent the conjoint movement of the other shifting sleeve half the shift actuator receptor  10  has on its side facing toward the shifting sleeve halves  8 ,  9  two grooves  15 ,  16  into which a displacement element  17  can be pressed. 
         [0039]    In addition the inner end faces of the shifting sleeve halves  8 ,  9  have chamfers  18  over which the displacement element  17  can be pressed into one of the two grooves  15 ,  16  when the shift actuator receptor is actuated; in the neutral position ( FIG. 3C ) the displacement element  17  is positioned between the two inner end faces of the shifting sleeve halves  8 ,  9 . 
         [0040]    When the left-hand gear is disengaged, due to the movement of the left shifting sleeve half  9  to the right by the chamfers  18  on the inside end faces of the shifting sleeve halves  8 ,  9  the displacement element  17 , which is preferably a ball, is pressed upward into a correspondingly shaped groove  16  in the shift actuator receptor  10 , as illustrated in  FIG. 3B . During this the right-hand shifting sleeve half  8  takes up the supporting force of the ball  17  and can rest against a retaining ring  29  or alternatively directly on the gearwheel  6 . 
         [0041]    When, now, the left gear is to be re-engaged, as shown in  FIG. 3A  the shift actuator receptor  10  is moved back to its central position again and during this the shifting sleeve half  9  is moved by the ball  17  to the left, the force required for synchronization and engagement being transmitted, according to the invention, by the ball  17 . On completion of the synchronization process the ball  17  is pressed back to its original position between the shifting sleeve halves  8 ,  9  (bottom right figure), which can be done by a spring force acting radially inward, while the simultaneous pressure on the ball  17  by the oblique faces in the groove  16  of the shift actuator receptor  10  assists this return process of the ball  17 . Preferably, the ball  17  is arranged in a spring ring. 
         [0042]    Alternatively to the design as a ball, the displacement element may have other shapes. For example, the displacement element can be shaped at the bottom (i.e. on its side facing away from the shift actuator receptor) as a cone and at the top (i.e. on its side facing toward the shift actuator receptor) as a cylinder or a square, and the grooves  15 ,  16  in the shift actuator receptor  10  are then adapted to match the shape of the displacement element. 
         [0043]    The embodiment shown in  FIGS. 3-3C  has the advantage of ensuring the best possible interlocking and forced disengagement and engagement processes. 
         [0044]      FIGS. 4 ,  5  and  6  show designs according to the invention of the shift element for the secure return movement of the displacement element  17 , even under the influence of centrifugal force. 
         [0045]      FIG. 4  shows a possibility for avoiding the sliding of the ball  17  along the chamfers of the shifting sleeve halves  8 ,  9  and the respective groove  15 ,  16  in the shift actuator receptor  10 . In this case the ball  17  is held in furrows  19  in the chamfers  18  of the shifting sleeve halves  8 ,  9  and the grooves  15 ,  16  in the shift actuator receptor  10  during the process of pressing back in or synchronization. This has the advantage that during synchronization a solid movement of the unit consisting of the shift actuator receptor/ball/shifting sleeve half occurs, which prevents sliding of the ball  17  along the oblique surfaces or chamfers  18 . 
         [0046]    The ball  17  must then be moved back into the space between the shifting sleeve halves  8 ,  9 , and this can be done for example by a ball/sprung joint ring such that the spring action pulls the ball  17  radially inward. 
         [0047]    Alternatively, as shown in  FIG. 5 , a spring leaf  20  with spring strips  21  can be inserted or arranged on the inside of the shift actuator receptor  10 . According to the invention the leaf  20  is secured against axial movement relative to the shift actuator receptor  10  by its contact on both sides against the inner sides of the carrier elements  11  of the shift actuator receptor  10 . 
         [0048]    When a ball or some other displacement element  17  moves radially into one of the grooves  15 ,  16  in the shift actuator receptor  10  (i.e. when a gear is disengaged), spring strips  21  on the spring leaf  20  are prestressed, and during the subsequent return and engagement of the gear these press the balls or displacement elements back again into the space between the shifting sleeve  8 ,  9 , while the sloping surfaces on the respective groove  15 ,  16  in the shift actuator receptor  10 , in passing across the balls or other displacement elements, additionally press them radially inward. 
         [0049]      FIG. 6  illustrates a further principle according to the invention for returning the ball or displacement element. In this case ejector teeth of an ejector tooth array  22  are arranged on the face of the gearwheels  6 ,  7  or on the clutch elements  2 , so that for example when the shift actuator receptor  10  is moved to the left in the central position, beyond a certain axial position of the shift actuator receptor  10  the teeth of the ejector tooth array  22  project into the shift actuator receptor  10  through apertures  23  provided for the purpose and so force the displacement element  17  to move radially inward and thus into the space between the shifting sleeve halves  8 ,  9 . 
         [0050]      FIG. 7  shows a shift element  1  made according to the invention, in which in order to avoid conjoint movement of the respective other shifting sleeve half  8  or  9  during a shift operation, a twisting motion is superimposed on the axial movement of the shift actuator receptor  10 . The twisting motion of the shift actuator receptor  10  is produced by means of oblique teeth  24  on the synchronizer element  4 , in which inner oblique teeth  25  of the shift actuator receptor  10  engage. The shift actuator is π-shaped and has a centrally positioned carrier  26  with the inner oblique teeth  25 , while its flanks form the carrier elements  11 . In the case when the shift element is configured as a claw-type shift element with no synchronizer rings, the oblique teeth  24  are located on part of the claw shift element that is fixed on the shaft. 
         [0051]    The operation of the shift element shown in  FIG. 7  is explained below with reference to  FIGS. 8A and 8B , considering the example “disengage and re-engage the gear on the left”. 
         [0052]    A gear is disengaged by the carrier elements  11  on the shift actuator receptor  10 . On the faces of the shifting sleeve halves  8 ,  9  and on the central carrier  26  of the shift actuator receptor  10  claws  27  are fixed on the surfaces, which in the central position shown in  FIG. 8A  must have a defined rotation position relative to one another. The representations in  FIGS. 8-8B  are plan views of the shift element  1 , sectioned through the shift actuator receptor  10 . 
         [0053]    When for example the left-hand gear is disengaged, the carrier element  11  on the shift actuator receptor  10  carries the left-hand shifting sleeve half  9  with it during its movement to the right. During this, the shift actuator receptor  10  is at the same time rotated relative to the synchronizer element  4  and the shifting sleeve halves  8 ,  9 , so that the angular position of the claws  27  relative to one another changes. 
         [0054]    In the example shown, to release the axial path the claws  27  on the right-hand side of the carrier  26  of the shift actuator receptor  10  come to rest directly next to the claws of the right-hand shifting sleeve half  8  ( FIG. 8B ), i.e. the axial distance between the shift actuator receptor  10  and the right-hand shifting sleeve half  8  (i.e. the one which is not to be shifted) has decreased (the right-hand shifting sleeve half has not been moved as well). 
         [0055]    The axial distance between the carrier  26  of the shift actuator receptor  10  and the left-hand shifting sleeve half  9  has not changed, but the angular position of the claws  27  of the two components  9 ,  26  has. In particular (see  FIG. 8B ) the claws  27  on the left side of the carrier  26  of the shift actuator receptor  10  rest directly against the ends of the claws  27  on the left shifting sleeve half  9 . 
         [0056]    When the gear on the left is to be re-engaged, as the shift actuator receptor  10  moves to the left (i.e. back to its central position) the claws  27  on the left of its carrier  26  press against the face of the left shifting sleeve half  9  to push it back toward the left into its initial position and thereby to synchronize and engage the gear ( FIG. 8 ). During this pushing movement a relative sliding movement on the end faces of the claws  27  takes place due to the rotation, so that at the end of the pushing movement the claws  27  are once again in their initial position shown in  FIG. 8A . 
         [0057]    In the example shown in  FIGS. 9 and 9A  too, a gear is disengaged by the axial movement of the carrier element  11  on the shift actuator receptor  10 . In this case the shift actuator receptor  10  is made radially springy, having strips  32  that spring out radially arranged at its circumference which can move radially outward when the shift actuator receptor  10  moves across whichever of the shifting sleeve halves remains stationary. 
         [0058]    This outward movement is accompanied by the rolling of balls  28  fitted into corresponding grooves  30 ,  31  in the springy strips in the shift actuator receptor and in the shifting sleeve halves  8 ,  9 . In  FIG. 9A  the shift element according to the invention is shown in its central position. 
         [0059]    When the left-hand gear is disengaged ( FIG. 9 ) the shift actuator receptor  10  is moved to the right and the balls  28  on the right side (i.e. the balls associated with the shifting sleeve half that is not to be shifted), on the one hand in the grooves  30  in the shift actuator receptor  10  and on the other hand in the grooves  31  of the shifting sleeve half  8  on the right, roll to the right, and at the same time move radially outward due to the special contour of the grooves  30 ,  31 . 
         [0060]    Owing to this radial movement and to the springy strips  32  attached at its periphery the shift actuator receptor  10  bends outward, which means that the right-hand shifting sleeve half  9  does not move as well. During this, the spring force acting via the balls  28  on the right-hand shifting sleeve  8  (i.e. the one not being shifted) is supported, according to the invention, on a retaining ring  29  or alternatively on the gearwheel  6 . 
         [0061]    When, now, the left-hand gear is re-engaged, as the shift actuator receptor  10  moves back to its central position it carries the balls  28  on the left and so also the left-hand shifting sleeve half  8  with it toward the left, whereby the left gear can be synchronized and re-engaged. Owing to the contour of the grooves, the right-hand shifting sleeve half  8  does not move as well even though the balls on the right move back to their initial position. In this case the spring force in the springy strips  32  of the shift actuator receptor  10  is designed to be large enough to hold the balls  28  securely in the grooves  30 ,  31  during the synchronization and engagement of the gear. 
         [0062]    A further advantageous embodiment of the invention is the object of  FIGS. 10 and 10A . This shift actuator receptor  10  is again π-shaped and its flanks form the carrier elements  11 . 
         [0063]    In this case, on the inside of the shift actuator receptor  10  is inserted a sheet  33  of spring steel with springy strips  34  projecting radially inward, which, when the shift element  1  is in its central position, rest against the inner end faces of the shifting sleeve halves  8 ,  9  ( FIG. 10A ). The springy strips  34  can in each case pivot in only one direction, namely toward the carrier element  11  for the shifting sleeve half associated with the springy strip  34  concerned. According to the invention, the sheet  33  is secured against axial movement relative to the shift actuator receptor  10  by its contact on both sides against the inner sides of the carrier elements  11  of the shift actuator receptor  10 . 
         [0064]    Below, the operating mode of the shift element shown in  FIGS. 10 and 10A  will be described considering the example “disengagement and re-engagement of the gear on the left”. The gear is disengaged by axial movement of the carrier elements  11  of the shift actuator receptor  10 . When, now, the left-hand gear is disengaged, the springy strip  34  in contact with the inside end face of the shifting sleeve  8  on the right moves (or bends) radially outward over the latter, so that the right shifting sleeve half  8  is not moved along during this. That is illustrated in  FIG. 10 . 
         [0065]    When the gear on the left is re-engaged by a movement of the shifting sleeve holder  10  to the left back to its neutral position, then the shift actuator receptor  10  carries the left-hand shifting sleeve half  9  along with it by virtue of the springy strip  34  bent down and resting against the left shifting sleeve half  9 . When the shift actuator receptor  10  has returned to its central position, the springy strip  34  on the right can bend radially inward so that the initial condition is reproduced. 
         [0066]    In the shift element shown in  FIGS. 11A and 11B  the conjoint movement of the torque-transmitting shifting sleeve half is prevented by the tilting of tilt-blocks  35  distributed on the periphery of the synchronizer element  4 , which also axially releases the shifting sleeve half to be disengaged. The shift actuator receptor  10  is again π-shaped, and its flanks form the carrier elements  11 . 
         [0067]    According to the invention, the tilt-blocks  35  are arranged in grooves  36  of the synchronizer element  4  in such manner that when they tilt, the ends of the tilt-blocks  35  pivot radially outward or inward. In addition, on the tilt-blocks  35  are provided carriers  37  which engage in grooves on the inside of the shift actuator receptor  10  so that when the shift actuator receptor  10  moves, the tilt-blocks  35  can pivot about their bearing-point in the synchronizer element  4 . In the central position the grooves  36  and the grooves  38  are positioned one above the other. In the case when the shift element is configured as a claw-type shift element without synchronizer rings, the grooves  36  are made in a component of the claw shift element arranged fixed on the shaft. 
         [0068]    Below, the operating mode of the shift element shown in  FIGS. 11-11B  will be explained considering the example “disengagement and re-engagement of the gear on the left”. The gear is disengaged by moving the carrier elements  11  of the shift actuator receptor  10  axially. The image in  FIG. 11A  shows the shift actuator receptor  10  in its central position. 
         [0069]    When, now, the left-hand gear is to be disengaged, as the left shifting sleeve half  9  is moved by the carrier element  11  on the shift actuator receptor  10  at the same time the tilt-blocks  35  also pivot. According to the invention, this pivoting process clears an axial path for the left shifting sleeve half  9  to be moved; it can now be disengaged without the tilt-blocks  35  blocking its path. Since the torque-transmitting shifting sleeve half  8  on the right does not move so that its distance from the pivot-point of the tilt-blocks  35  does not change, the right-hand portion of the tilt-blocks  35  can pivot radially inward past the right shifting sleeve half  8  without impediment, as shown in  FIG. 11B . 
         [0070]    If, now, the left-hand gear is to be re-engaged, as shown in  FIG. 11  the shift actuator receptor  10  is moved back to its central position so that the tilt-blocks  35  pivot back to their initial position. However, during this pivoting of the tilt-block  35  they come in contact with the disengaged, left-hand shifting sleeve half  9 . As the shift actuator receptor  10  moves farther to the left, the returning tilt-blocks  35  push the left shifting sleeve half  9  to the left, so synchronizing and engaging the left-hand gear. Preferably, the inner end faces of the shifting sleeve halves  8 ,  9  have chamfers  39  to facilitate the contact conditions. 
         [0071]    Another example of a shift element  1  according to the invention is the object of  FIGS. 12A ,  12 B and  12 C. In this case, analogously to the example embodiment shown in  FIGS. 11-11B , the conjoint movement of the torque-transmitting shifting sleeve half is prevented in that pivoting elements  40  are provided, which are rotated to clear an axial path for the shifting sleeve half to be disengaged. In contrast to the example embodiment according to  FIGS. 11-11B , the rotation axes of the pivoting elements  40  extend radially outward, i.e. the rotation planes of the pivoting elements  40  are tangential to the periphery of the synchronizer element  4 ; according to the invention, the pivoting elements  40  are mounted to rotate in the synchronizer element  4 . In the case that the shift element is configured as a claw-type shift element without synchronizer rings, the pivoting elements  40  are mounted on a part of the claw shift element arranged fixed on the shaft. 
         [0072]      FIGS. 12A and 12C  show, respectively a sectioned view and a plan view of a section through the shift actuator receptor  10  of the shift element in its central position;  FIGS. 12 and 12B  show, respectively, a sectioned view and a plan view of a section through the shift actuator receptor  10  when the left-hand gear has been disengaged. 
         [0073]    When the shift actuator receptor  10  moves to the right, the left shifting sleeve half  9  is carried with it by the left-hand carrier element  11  on the shift actuator receptor  10 , so that the pivoting elements  40 , which engage by means of carriers  41  in grooves  42  on the inner side of the shift actuator receptor  10 , are rotated out of their initial position. This releases an axial path to enable the left-hand shifting sleeve half  9  to be disengaged ( FIGS. 12 and 12B ). 
         [0074]    When the shift actuator receptor  10  moves back to its central position, the pivoting elements  40  too turn back to their starting position and, during this, press on the left shifting sleeve half  9  so as to push it back to the left, whereby the left-hand gear is synchronized and engaged. 
         [0075]    Needless to say, any design configuration and in particular any spatial arrangement of the components of the shift element according to the invention, per se and in relation to one another and provided they are technically appropriate, are covered by the protective scope of the present claims, without influencing the function of the shift element as indicated in the claims, even if such configurations are not represented explicitly in the figures or in the description. 
       Indexes 
       [0000]    
       
           1  Shift element 
           2  Clutch element 
           3  Synchronizer ring 
           4  Synchronizer element 
           5  Shifting sleeve 
           6  Gearwheel 
           7  Gearwheel 
           8  Shifting sleeve half 
           9  Shifting sleeve half 
           10  Shift actuator receptor 
           11  Carrier element 
           12  Spring element 
           13  Spring element 
           14  Carrier of the shift actuator receptor 
           15  Groove 
           16  Groove 
           17  Displacement element 
           18  Chamfer 
           19  Furrow 
           20  Spring sheet 
           21  Springy strip 
           22  Ejector teeth 
           23  Aperture 
           24  Oblique teeth on the synchronizer element 
           25  Inner oblique teeth on the shift actuator receptor 
           26  Carrier of the shift actuator receptor 
           27  Claw 
           28  Ball 
           29  Retaining ring 
           30  Groove 
           31  Groove 
           32  Strip 
           33  Sheet 
           34  Springy strip 
           35  Tilt-block 
           36  Groove 
           37  Carrier 
           38  Groove 
           39  Chamfer 
           40  Pivoting element 
           41  Carrier 
           42  Groove