Patent Publication Number: US-2004055405-A1

Title: Synchronizing system

Description:
[0001] The invention relates to a synchronizing system for manual transmissions, having a gear, a shift sleeve which is displaceably in engagement with the gear, and with thrusters arranged between the gear and the shift sleeve which have each a box-like casing held in an axial groove in the gear, and a spring which is supported on the bottom of the thruster casing and biases a detent against the internal teeth of the shift sleeve.  
       [0002] Synchronizing systems serve in manual transmissions for producing a synchronism between two gears mounted on a common shaft before a driving connection is produced between these gears. For this purpose a synchronizing ring is provided between the drive gear on the shaft and the driven gear mounted for rotation on the shaft, and can be urged into frictional engagement with the driven gear. When the shift sleeve on the driving gear is shifted toward the driven gear, its internal teeth run first against beveled teeth of the synchronizing ring, so that a frictional face of the synchronizing ring is urged against the driven gear. As long as the rotatory speed of the driving and driven gears are not the same, the torque exerted by the friction produced by the contact with the synchronizing ring prevents any further displacement of the shift sleeve. Only when the rotary speeds are equal can the synchronizing ring rotate relative to the shift sleeve to a position wherein the shift sleeve can be shifted against external teeth on the driven gear, so that the driven gear is coupled torsionally to the driving gear. The thrusters arranged between the driving gear and the shift sleeve eliminate the free play between the driving gear and the shift sleeve and thus contribute to the reduction of noise and wear.  
       [0003] In DE 195 80 558 C1 a synchronizing system of this kind is described, in which the axial grooves serving to accommodate the thrusters have a T-shaped profile. The housings of the thrusters have a shape complementary to this profile and are supported on the shoulders of the T-shaped groove near the end that is provided with the thruster. Thus the thrusters are guided for displacement in the grooves. The thrusters are biased by the springs into recesses in the internal teeth of the drive gear. When the shift sleeve is shifted the thrusters are first carried a short distance until they abut against the synchronizing ring. Only then are the thrusters forced back against the force of the spring, so that the shift sleeve can be shifted further by overcoming the slight resistance of a catch. The manufacture of the T-shaped grooves, however, is relatively expensive. Moreover, a relatively great amount of space is required to accommodate the thrusters, and due to the grooves widened at the radially outer ends the external teeth of the gear are interrupted on a relatively great circumferential length. Furthermore, as the thrusters shift, friction and wear occur because the widened heads of the casings are driven by the springs with great force against the shoulders of the T-slots.  
       [0004] It is therefore the object of the invention to create a synchronizing system, which can be manufactured more easily, will permit a compact construction of the synchronizing system, and permit easy movement of the shift sleeve.  
       [0005] This object is achieved by the fact that the casing of the thruster is supported in such a manner as to be able to tilt on the bottom of the groove in the gear.  
       [0006] Upon the movement of the shift sleeve, the casings of the thrusters are thus not shifted as a whole relative to the gear, but only rocked slightly on their radially interior ends, so that they do not hamper the movement of the shift sleeve. At the same time, this design permits the grooves in the gear to be made narrower and with a simple rectangular profile. Accordingly, the thruster casings can also have a simpler form and smaller dimensions circumferentially about the gear.  
       [0007] Advantageous embodiments of the invention are described in the sub-claims.  
       [0008] The casing of the thruster is preferably made of plastic and at the end, which receives the thruster, a ball catch for example, an abutment is formed which secures the ball catch against escape. The bottom of the casing is preferably slightly rounded, so that it can roll on the bottom of the groove in the gear during the tilting movement.  
       [0009] The thruster casing can be in the shape of a square post, but optionally it can be slightly thicker at its radially outer end in the axial direction of the gear. If a thruster casing is in the shape of a square post, the bottom can be rounded spherically, so that the casing can be inserted into the groove in the gear optionally in positions rotated 90° away from one another. In this manner errors are avoided when equipping the gear with the thrusters.  
       [0010] Preferably, the thruster casing has extensions at its radially outer end, which engage the gaps between the internal teeth of the shift sleeve. In this case, in the event that the spring of the shift sleeve breaks, or the catch body is lost or jams, the shift sleeve can be still supported by the projections of the casing, so that even in this case any chattering between the shift sleeve and the gear can be prevented. 
     
    
    
     [0011] Embodiments of the invention are described hereinafter with the aid of the drawing, in which  
     [0012]FIG. 1 shows a section through a synchronizing system in the neutral position,  
     [0013]FIG. 2 shows a view of a shift sleeve on a gear provided with thrusters and represented in section,  
     [0014]FIG. 3 shows an enlarged sectional representation of the thrusters from FIG. 2,  
     [0015]FIG. 4 shows a side view of the thruster,  
     [0016]FIG. 5 shows a section taken along line V-V in FIG. 4,  
     [0017]FIG. 6 shows a thruster in a plan view;  
     [0018] FIGS.  7  to  9  show a side view, a longitudinal section and a plan view of a thruster of another embodiment;  
     [0019]FIGS. 10 and 11 show sectional drawings similar to FIG. 1 for different positions of the synchronizing system, and  
     [0020]FIGS. 12 and 13 show longitudinal sections of two thrusters of two additional embodiments. 
    
    
     [0021]FIG. 1 shows a gear  12  splined on a shaft  10  and surmounted by a shift sleeve  14 . With internal teeth  16  the shift sleeve engages the teeth of the gear  12  and is displaceable on the gear in the axial direction of the shaft  10 .  
     [0022] On both sides of the gear  12  and the shift sleeve synchronizing rings  18  and  20  are arranged which rotate together with the gear  12  and the shift sleeve  16 , but are able to rotate relative to the gear  12  within a limited angular range. On the side of synchronizing ring  20  opposite the gear there is shown a gear  22  which is mounted for rotation on the shaft  10  and can be coupled by the shift sleeve  14  to the gear  12  to rotate with the latter. On the side of the other synchronizing ring  18  facing away from the gear  12  there is an additional gear with a different diameter, which is not shown. By the displacement of the shift sleeve  14  in one or the other direction, either the gear  22  or the additional gear not shown can be driven by the shaft  10 , so that different ratios can be established in the transmission.  
     [0023] As it can be seen in FIG. 2, the gear  12  has in its outer circumference three slots  24  which are continuous in the axial direction, and are arranged at 120° apart; they have an elongated cross section in the radial direction and interrupt the external teeth of the gear  12  at the point of a single tooth. Thrusters  26  are inserted into the slots  24 , only one of which is shown in FIG. 2. In FIG. 1 the section plane passes through the upper slot  24  into which the thruster  26  is inserted. The thruster  26  bears a ball which is referred to hereinafter as detent ball  28  and which is resiliently biased radially outward and, as FIG. 1 shows, it engages a shallow, trough-like recess  30  formed in one of the teeth of the shift sleeve  14 .  
     [0024] The thruster  26  is shown in greater detail in FIGS.  3  to  6 . It has a box-like thruster casing  32  formed by a plastic molding, which is in the shape of a rectangular, approximately square post. In the sectional drawing of FIG. 3 and the elevation in FIG. 4 the casing  32  has a width which corresponds to the width of the slots  24 . In the direction perpendicular thereto (sectional drawing of FIG. 5) the width of the casing is slightly smaller. Inside of the casing a cylindrical bore is formed which accommodates a spring  34 . The spring  34  is supported on the bottom  36  of the thruster casing  32  and biases the detent ball  28  upwardly against the shift sleeve. The detent ball  28  is contained for displacement in an expanded upper portion of the bore, but is permanently held in the casing against escape by slight crimping  38  on the somewhat thinner walls of the casing  32  shown in section in FIG. 5. During assembly the detent ball  28  can thus be snapped into the casing  32 , so that the thruster can then be inserted as a preassembled unit into the gear  12 . Near the bottom  36  of the casing holes  40  (FIG. 5) are provided for drainage of transmission oil.  
     [0025] As it is furthermore to be seen in FIG. 5, the bottom  36  of the thruster casing  32  is slightly rounded.  
     [0026] The walls of the thruster casing  32  shown in section in FIG. 3 form projections  42  which protrude above the crimps  38  and thus define an opening  44  (FIG. 4) which can be engaged by a tooth provided with the recess  30  on the shift sleeve  14 .  
     [0027] FIGS.  7  to  9  show the thruster  26 ′ which differs from the thruster  26  previously described, in that the casing  32  has on the radially outer (upper in FIGS.  7  to  8 ) end a thickened head  46  of longitudinal rectangular plan which extends in the direction of the axial slot  24 . In this manner a better guidance of the casing  32  in the slot  24  is obtained, and at the same time greater rigidity in the crimps  38 .  
     [0028] On both of the thrusters  26  and  26 ′ the projections  42  are rounded at the top, as it can be seen in FIGS. 5 and 8. The rounding corresponds to an arc that is concentric with the bottom crest of the rounding of the bottom  36 .  
     [0029] The manner of the operation of the synchronizing system is now to be explained with the aid of FIGS. 10 and 11.  
     [0030] In FIG. 10 the shift sleeve  14  is shifted slightly rightward in comparison with FIG. 1, so that the internal teeth  16  run on slopes of external teeth of  48  of the synchronizing ring  20 . In this movement of the shift sleeve  14  the thruster  26  is rocked over about its bottom end which rests on the bottom of the slot  24 . This rocking is facilitated by the rounding of the bottom  36  of the casing  32 . Due to this tilting movement the ball detent  28  remains engaged with the recess  30  of the shift sleeve. In the state shown in FIG. 10, the tilting of the thruster  26  is limited by the fact that its casing  32  collides with the synchronizing ring  20 .  
     [0031] In the movement of the shift sleeve  14  between the positions shown in FIGS. 1 and 10 there is thus no need to overcome any frictional resistance, since the thrusters  26  act equally as joints which permit the relative movement between gear  12  and shift sleeve  14  and at the same time always allow for free play.  
     [0032] The synchronizing ring  20  in the state shown in FIG. 10 has been shifted by a conical friction surface against an external taper  50  of gear  22 , so that gear  22  is accelerated or retarded by friction to the rotatory speed of the unit formed by gear  12 , shift sleeve  14  and synchronizing ring  20 . As long as equality of speed is not reached, the tooth slopes of the external teeth  48  of the synchronizing ring  20 , which is then still subject to a high torque, offer so much resistance to the movement of the shift sleeve  14  that the internal teeth  16  still cannot be brought into engagement with external teeth  52  of gear  22 . Not until the speeds become equal can the shift sleeve  14  be shifted further into the position shown in FIG. 11, in which it produces a coupling action between gears  12  and  22 . Since the detent ball  28  can no longer participate in this further movement of the shift sleeve  14 , it is forced out of the recess  30  in the shift sleeve against the force of the spring  34 . When gear  22  is coupled with gear  12  a detent resistance produced by the thrusters  26  has to be overcome.  
     [0033] Furthermore, the movement of the shift sleeve  14  is controlled by a shift fork not shown, which engages the groove  54  on the outer circumference of the shift sleeve. The shift sleeve is also held in the positions shown in FIGS. 1 and 11 by this shift fork.  
     [0034] By the rounding of the projections  42  of the casing  32  of the thruster  26 , and especially of thruster  26 ′, it is assured that the casing will not collide against the internal teeth  16  of the shift sleeve due to the tilting movements, so that only the detent ball  28  comes in contact with the shift sleeve. As shown in FIG. 2, however, the projections  42  reach so far into the gaps between the internal teeth  16  that the casing  32  of the thruster  26  can act also independently of the detent ball  28  as a spacer between the gear  12  and the shift sleeve  14 , and thus it prevents tooth chatter in case of a broken or excessively weak spring  34 .  
     [0035] In a modified embodiment of the thruster  26 , which is not shown, the plan of its casing  32  can also be precisely square, and in the casing walls which form the projections  42 , recesses similar to recesses  44  can be provided. In this case the thruster  26  is spherically rounded on its bottom  36  and has a generally 90° symmetry about its longitudinal axis, so that it can be inserted into groove  24  in any desired position.  
     [0036] Since the slots  24  of the gear are continuous in the axial direction, the thrusters  26  and  26 ′ are easy to install. Although the slots  24  are open at both ends the thrusters cannot drop out because they are secured in position by the synchronizing rings  18  and  20 .  
     [0037]FIGS. 12 and 13 show thrusters  26 ″ and  26 ′″ which differ from the thrusters  26  and  26 ′ in that they are secured at their bottom  36  against slipping in the slot  24  of the gear  12 . The thruster  26 ″ has a recess  56  which is engaged by a projection  58  protruding from the bottom of slot  24 . The thruster  26 ′″ has a projection  60  which engages a groove  62  on the bottom of slot  24  of gear  12 . The projections  58  and  60  and recesses  56  and  62  are matched to one another such that they permit the tilting of the thruster in the plane of drawing of FIG. 12 and FIG. 13.