Patent Publication Number: US-2023140319-A1

Title: Claw-type gearshift and method of shifting a claw-type gearshift

Description:
TECHNICAL FIELD 
     The disclosure relates to a claw-type gearshift and a method of shifting a claw-type gearshift. The claw-type gearshift is provided in particular for a manual transmission of a vehicle. 
     BACKGROUND 
     Claw-type gearshifts, i.e. shiftable claw clutches, have the drawback in motor vehicles that vibrations and noise may occur during engagement of the two coupling elements with each other when there are rotational speed differences. 
     The object of the disclosure is to provide a claw-type gearshift in which noise generation and wear are reduced. 
     SUMMARY 
     The claw-type gearshift according to the disclosure includes a sliding sleeve which is adapted to be axially displaced on a hub body and has an internal toothing having a multitude of sliding sleeve teeth, and a clutch body of a speed change gear, which has an external toothing which has a multitude of clutch body teeth and is adapted to engage in the internal toothing of the sliding sleeve. Arranged on the hub body is at least one thrust piece which is coupled to the sliding sleeve and includes a friction surface that cooperates with a mating friction surface on the clutch body. The thrust piece is displaceable in relation to the hub body in the circumferential direction by a certain degree between a release position and two locking positions, the locking positions being located on either side of the release position in the circumferential direction. The thrust piece includes a first locking structure which cooperates with a second locking structure on the internal toothing of the sliding sleeve, the locking structures being configured such that in each of the locking positions, the locking structures rest against each other such that a further axial movement of the sliding sleeve is blocked. 
     Similar to a synchronizer ring of a known synchronized gearshift, the thrust pieces in this entirely different application prevent the sliding sleeve from striking the clutch body at a high differential speed. The thrust pieces allow the sliding sleeve toothing to engage with the clutch body toothing only after an adaption of the speeds, which, however, is preferably not performed by the thrust pieces themselves, but away from the claw-type gearshift. In this way, noise generation and component wear are significantly reduced. 
     The thrust pieces here take over the function of a synchronizer ring in known synchronized gearshifts. The claw-type gearshift therefore advantageously comprises neither a synchronizer ring nor a blocking ring. 
     The thrust pieces preferably each include a spring-loaded ball which is radially displaceable in a known manner and which provides for the initial axial deflection of the thrust piece by the sliding sleeve and which is pressed radially into the thrust piece by the sliding sleeve when the sliding sleeve is displaced toward the speed change gear so far that the internal toothing of the sliding sleeve engages with the external toothing of the clutch body. These balls, however, are preferably not involved in locking the sliding sleeve. 
     Generally, there is no provision for the sliding sleeve to actively return the thrust pieces to their release position in order to allow an engagement. The thrust pieces preferably constitute a form-locking blockade for the sliding sleeve against displacement of the sliding sleeve teeth between the clutch body teeth when an axial shifting force is applied in the non-synchronized state. To this end, in particular, the locking structures are configured such that the sliding sleeve cannot return the thrust pieces to the release position when a shifting force is applied axially. 
     For example, the first locking structure on the thrust piece includes two axially limited and oppositely oriented recesses that are open in the circumferential direction, and the second locking structure on the internal toothing of the sliding sleeve is formed by radial tooth extensions, wherein in each of the locking positions a respective tooth extension engages in one of the recesses. The axial delimitation of the recesses prevents an axial movement of the tooth extension and thus of the entire sliding sleeve. 
     The tooth extensions are provided, for example, to limit a shifting travel toward the clutch body, that is, they fulfill a dual function in that they also act as a locking structure. 
     In order to be able to move between the locking positions and the release position, the thrust pieces are received in the hub body so as to be movable to a certain degree in the circumferential direction. For example, the thrust pieces are each received in a retainer in the hub body, the retainer being designed to be so large that it allows a displacement of the thrust piece in the circumferential direction into both locking positions. 
     The range of movement of the thrust pieces in the circumferential direction preferably comprises half an angular distance between neighboring sliding sleeve teeth, so that the tooth extension can both engage in and slide completely out of the recess. 
     In addition, the thrust pieces are movable in the axial direction to such an extent that the thrust pieces can be brought into contact with the clutch body by the sliding sleeve. 
     Restoring the thrust pieces is preferably effected by a rotational speed crossing, i.e. a change in direction of the relative rotational speed of the clutch body and the hub body after a zero crossing. 
     There are two possible scenarios for this. For one thing, the relative rotational speed experiences a change in direction when one component, that is, the clutch body or the hub body, which was previously leading the other, now lags behind it, but both components retain their previous absolute direction of rotation. For another thing, the relative rotational speed also changes direction when one of the components, that is, the clutch body or the hub body, changes its absolute direction of rotation. 
     In either case, the frictional torque also undergoes a change of direction. 
     The friction surface preferably forms a portion of a conical surface, while the mating friction surface is circumferentially conical all around to provide a sufficiently high frictional force. 
     Preferably, the friction surface is formed on a lower surface of the thrust piece. 
     Since in a claw clutch the sliding sleeve teeth and the clutch body teeth are normally formed without engagement slopes, the required axial installation space for the claw-type gearshift is reduced. 
     Generally, the friction surface and/or the mating friction surface may be formed only by the surface of the material of the thrust piece or of the clutch body, with a suitable structuring, if required, for example a grooved structure. In addition, one or both friction surfaces may also be provided with a friction-enhancing and/or wear-reducing coating. 
     The above-mentioned object is also achieved by a method of shifting a claw-type gearshift, in particular a claw-type gearshift as described above. The claw-type gearshift includes a sliding sleeve which is adapted to be axially displaced on a hub body and a clutch body of a speed change gear, which is adapted to move into engagement with the sliding sleeve, wherein arranged on the hub body is at least one thrust piece which is adapted to be deflected axially and in the circumferential direction and which includes a friction surface adapted to come into contact with a mating friction surface on the clutch body. A difference in speed of the clutch body and the hub body is reduced. When the thrust piece is deflected axially, the friction surface of the thrust piece comes into contact with the mating friction surface of the clutch body. The thrust piece is displaced to one of the locking positions in the circumferential direction by the frictional connection with the clutch body, wherein a further axial movement of the sliding sleeve is prevented by the engagement of the first locking structure on the thrust piece with the second locking structure on the sliding sleeve. Subsequently, the thrust piece is returned to the release position in the circumferential direction by the frictional connection when a change in direction of the relative rotational speeds of the clutch body and the hub body occurs, and the internal toothing of the sliding sleeve is engaged with the external toothing of the clutch body. 
     Restoring the thrust piece to the release position is effected exclusively by the thrust piece(s) being entrained by the clutch body or the hub body when one of these components experiences a rotational speed crossing. 
     As long as the hub body and the clutch body rotate in the same direction at different speeds, the thrust pieces preferably block an axial further movement of the sliding sleeve irrespective of the shifting force acting. 
     If a tooth-on-tooth position occurs at the first contact between the sliding sleeve teeth and the clutch body teeth, a relative rotation between the hub body and the clutch body, which allows the internal toothing of the sliding sleeve to engage with the external toothing of the clutch body, is advantageously achieved by a speed difference between the hub body and the clutch body that builds up after rotational speed crossing. Typically, a small speed difference necessarily appears after only a short time following rotational speed crossing. Therefore, the clutch body and the sliding sleeve will automatically move to a tooth-on-gap position. 
     At this point in time, the thrust piece is already in its release position and no longer blocks the sliding sleeve. It is also of advantage that the speed adaption need not be designed such that it results in completely identical speeds of the hub body and the clutch body. 
     In particular, the adaption of the speeds of the hub body and the clutch body is not performed by the thrust piece(s), but through a device that is separate from the thrust piece and can be implemented at a suitable location in the vehicle away from the claw-type gearshift. 
     The speed adaption is preferably initiated before the shifting force is applied and the sliding sleeve is moved, so that the thrust piece does not come into contact with the clutch body until the speeds have already been largely matched. The frictional connection between the thrust piece and the clutch body therefore only has to withstand very small speed differences, so that the design of the thrust piece and its retainer in the hub body can be essentially adopted from known thrust pieces. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows a schematic exploded view of a claw-type gearshift according to the disclosure for carrying out a method according to the disclosure; 
         FIG.  2    shows a schematic partly sectional view of the claw-type gearshift of  FIG.  1   ; 
         FIGS.  3  and  4    show schematic perspective views of the locking structures on the thrust piece and on the sliding sleeve; 
         FIGS.  5  and  6    show schematic views of the claw-type gearshift from  FIG.  1    in a neutral position, the thrust piece being in its release position; 
         FIGS.  7  and  8    show schematic views of the claw-type gearshift from  FIG.  1    in a locked position, with the thrust piece in one of its locking positions; and 
         FIGS.  9  and  10    show schematic views of the claw-type gearshift from  FIG.  1    in a docking position, in which the thrust piece is in the release position and the sliding sleeve is in engagement with the clutch body. 
     
    
    
     DETAILED DESCRIPTION 
     For the sake of clarity, where components are shown more than once in the drawings, not all of them are provided with reference numbers. 
     The claw-type gearshift  10  illustrated in the figures, which is designed here for a manual transmission of a motor vehicle, serves to optionally connect a rotatable shaft to a speed change gear (not shown) for joint rotation therewith. The shaft carries a hub body  12 , which is connected to said shaft for joint rotation therewith, while a clutch body  14  is permanently attached to the speed change gear for joint rotation therewith. 
     The hub body  12  includes an external toothing  16  that is permanently in engagement with an internal toothing  18  of a sliding sleeve  20  that surrounds the hub body  12  in the circumferential direction U. 
     The sliding sleeve  20  is displaceable in the axial direction A by a certain degree to either side of the hub body  12 , with the toothings  16 ,  18  remaining in engagement with each other at all times. The sliding sleeve  20  is axially displaceable so far that the internal toothing  18  comes to engage with an external toothing  22  of the clutch body  14 . 
     As is illustrated in  FIG.  1   , generally two speed change gears, each with a clutch body  14 , are arranged on either side of the hub body  12  so that two gears can be shifted by the axial movement of the sliding sleeve  20 . 
     In a circumferential surface of the hub body  12 , a plurality of thrust pieces  23 , in this case three, are arranged so as to be evenly distributed over the circumference, which are each accommodated in a radial retainer  24  and which are movable to a certain degree in both directions both in the axial direction A and in the circumferential direction U. 
     Accommodated in each of the thrust pieces  23  is a so-called locking block  26 , which can be pressed into the thrust piece  23  in the radial direction r against a spring tension. With respect to the movement in the axial direction A, the thrust pieces  23  cooperate with the sliding sleeve  20  in a known manner. In a neutral position, the locking blocks  26  each engage in a latching groove  28  on the inside of the sliding sleeve  20 , so that the thrust pieces  23  are deflected axially when the sliding sleeve  20  is displaced (see  FIGS.  7  and  8   ). When the internal toothing  18  of the sliding sleeve  20  engages the external toothing  22  of the clutch body  14 , the locking blocks  26  are pressed into the respective thrust piece  23  so that the sliding sleeve  20  can slide thereover (see  FIGS.  9  and  10   ). 
     In this example, all three thrust pieces  23  are of identical structure. 
     On the surface that fits into the external toothing  16  of the hub body  12 , each of the thrust pieces  23  has a first locking structure  30  that cooperates with a second locking structure  32  on the internal toothing  18  of the sliding sleeve  20  to block an axial movement of the sliding sleeve  20  in the locked position of the claw clutch  10 . 
     The first locking structure  30  is formed here by two opposing recesses  34  which are open in the circumferential direction U and are each bounded axially by a web  38 . The sides of the webs  38  that face the recess  34  extend in the circumferential direction U. 
     The second locking structure  32  here consists of a respective tooth extension  39  on each of the sliding sleeve teeth  36  that are adjacent to the tooth having the latching groove  28  (see  FIG.  4   ). Each tooth extension  39  projects radially beyond the rest of the sliding sleeve tooth  36 . The axial length of the recesses  34  is coordinated with the axial length of the tooth extensions  39  such that the latter can fully lie in the recess  34  in the axial direction A. 
     In the circumferential direction U, the recesses  34  are each spaced apart from the next sliding sleeve tooth  36  by half a tooth spacing of the sliding sleeve toothing  18  in the neutral position of the claw clutch  10 . 
     The tooth extensions  39  perform a dual function here, in that they also serve as a stop in a known manner to specify the depth of engagement between the sliding sleeve toothing  18  and the clutch body toothing  22  and thus to limit the shifting travel of the sliding sleeve  20 . 
     At its axial edges, each thrust piece  23  includes a friction surface  42 , which here is arranged on the lower side of the thrust piece  23 . 
     The friction surfaces  42  are part of a conical surface which is adapted in shape to a conical surface on the respective clutch body  14 , on which a mating friction surface  44  is formed (see, for example,  FIGS.  1  and  2   ). 
     The retainer  24  in which the thrust piece  23  is received in the hub body  12  is configured such that the respective thrust piece  23  has sufficient clearance in the axial direction A that it can be displaced to the clutch bodies  14  so far in both directions until the friction surface  42  moves into frictional contact with the mating friction surface  44 . 
     In the circumferential direction U, the clearance for movement of the thrust piece  23  in the retainer  24  between two side surfaces  46 , which delimit the retainer  24  in the circumferential direction U, is larger and selected such that the thrust piece  23  can move from a central neutral position in either direction by an angular distance of α/ 2  between two sliding sleeve teeth  36 . This distance is dimensioned such that the tooth extensions  39  can engage in and completely leave the recesses  34  again (see, for example,  FIGS.  6 ,  8  and  10   ). 
     In this way, the thrust pieces  23  can move from a central release position, in which none of the tooth extensions  39  engages in a recess  34 , to two opposite locking positions, in which a respective one of the tooth extensions  39  is located in one of the recesses  34 . 
     The toothings  18 ,  22  of the sliding sleeve  20  and the clutch body  14  include dimensions that are matched to each other so that the sliding sleeve teeth  36  can engage between the clutch body teeth  40 . 
     Both the sliding sleeve teeth  36  and the clutch body teeth  40  are formed completely without engagement slopes. 
     Referring to  FIGS.  5  to  10   , the operation of the claw-type gearshift  10  will now be described. 
       FIGS.  5  and  6    show the claw-type gearshift  10  in a neutral position. 
     The sliding sleeve  20  inclusive of the thrust pieces  23  and the clutch body  14  are axially spaced apart from each other and do not touch. The sliding sleeve  20  is positioned centrally between the two clutch bodies  14 . The sliding sleeve teeth  36  are located in the gaps of the toothing  22  in the circumferential direction U. The tooth extensions  39  are located outside the recesses  34 . 
     For shifting a gear, the speeds of the hub body  12  and the clutch body  14 , which is to be coupled to the sliding sleeve  20 , are first largely equalized by a device  48  for speed adaption (shown schematically in  FIG.  2   ). The device  48  may, for example, be coupled to an electric motor of the vehicle and does not comprise the thrust pieces  23 . 
     Only when this substantial speed adaption has been effected is an axial shifting force F applied, to the right in the Figures. The sliding sleeve  20  is displaced a short distance in the axial direction A, deflecting the locking blocks  26  in the process, which in turn entrain the thrust pieces  23  in the axial direction A until the friction surface  42  on the thrust piece  23  moves into frictional contact with the mating friction surface  44  on the clutch body  14  of the speed change gear to be shifted. 
     Since the hub body  12  and the clutch body  14  rotate at different speeds, the thrust pieces  23  are entrained in the circumferential direction U by the frictional forces between the friction surface  42  and the mating friction surface  44 . In the process, the thrust pieces  23  flip from the central release position into one of the two locking positions. The rotation of the thrust pieces  23  is limited by the side surfaces  46  of the retainer  24  in the hub body  12 . 
     The relative movement of the thrust pieces  23  in relation to the internal toothing  18  of the sliding sleeve  20  causes the tooth extension  39  of one of the sliding sleeve teeth  36  to move into the recess  34  on both sides of the sliding sleeve tooth  36  which includes the latching groove  28 . 
     The sliding sleeve  20  is therefore prevented from further axial movement by the webs  38  axially bounding the recess  34 . 
     The claw-type gearshift  10  is now in its locked position, in which the sliding sleeve  20  cannot move further toward the clutch body  14  in the axial direction A. 
     It is not intended that the sliding sleeve  20  can actively rotate the thrust pieces  23  back to their release position. The sides of the webs  38  facing the recess  34  are oriented such that the sliding sleeve teeth  36  cannot generate a sufficient force component in the circumferential direction U to result in a rotation of the thrust piece  23 . When the thrust pieces  23  are in one of the locking positions, the sliding sleeve  20  is prevented from moving axially further to the associated clutch body  14 , irrespective of the axial shifting force F applied. 
     The thrust pieces  23  here do not perform the task of speed adaption between the hub body  12  and the clutch body  14 , which is effected practically exclusively by the device  48 . 
     The device  48  further acts to adapt the speeds of the hub body  12  and the clutch body  14 . In this process, after a short period of time, a rotational speed crossing will occur, that is, a change in direction of the relative rotational speed of the hub body  12  and the clutch body  14 . 
     This change in the direction of rotation causes the thrust pieces  23  to flip back to the release position in the circumferential direction U, resulting in the docking position shown in  FIGS.  9  and  10   . The tooth extensions  39  are located next to the recesses  34  in the circumferential direction U. 
     The sliding sleeve  20  can now be moved further in the axial direction A, with its internal toothing  18  engaging with the external toothing  22  of the clutch body  14 . 
     The rotational speed crossing is also always associated with the build-up of a new, small difference in speed between the hub body  12  and the clutch body  14 . This ensures that the sliding sleeve  20  and the clutch body  14  automatically move to a position in which the sliding sleeve teeth  36  meet the gaps in the external toothing  22  of the clutch body  14 , even if there should be a tooth-on-tooth position at the first contact. 
     The thrust pieces  23  are not involved in this process. 
     While having a compact axial type of construction, the claw-type gearshift  10  allows a low-noise and low-wear shifting, since the movement of the sliding sleeve  20  is blocked as a result of the circumferential displacement of the thrust pieces  23  until a rotational speed crossing has taken place. However, the thrust pieces  23  are not made use of for speed adaption here.