Abstract:
A transmission shift system comprising a synchronizing device for idler wheels, which can be actuated hydraulically and comprises at least one piston that can mesh with a selected idler wheel as the sliding sleeve. The piston can be displaced axially on a shaft via a hydraulic actuation and is non-rotatably connected with it, thus self-locking synchronization is provided.

Description:
This application is a national stage completion of PCT/EP2003/006734 filed Jun. 26, 2003 which claims priority from German Application Serial No. 102 29 515.8 filed Jul. 2. 2002. 
   FIELD OF THE INVENTION 
   The present invention relates to a transmission shift system for idler wheels. 
   BACKGROUND OF THE INVENTION 
   From the state of the art, transmission shift systems for idler wheels are known. In the familiar transmission shift systems generally synchronizing devices are provided for the purpose of synchronizing the idler wheels, wherein the devices actuate the sliding sleeves mechanically in order to synchronize the desired idler wheel with a shaft. 
   From the publication DE 43 24 814 A1, a transmission with a lock synchronization arrangement is known, wherein a synchronizer member that is connected to a transmission shaft and at least one gear wheel rotating at a different speed can be positively coupled during synchronous speed with the help of an annular sliding sleeve that is axially displaceable by the gearshift force. A synchronizer ring is provided, between the sliding sleeve and each gear wheel, wherein parts of the synchronizer ring form a positively engaged coupling with parts of the gear wheels. In the absence of synchronization, the axial movement of the sliding sleeve is blocked by blocking surfaces of locking teeth. In such a transmission, the synchronization is also shifted mechanically via the sliding sleeve. 
   The publication DE 37 11 490 C2 discloses a gear shifting device. In this gear shifting device, the sliding sleeve is actuated by an adjusting arrangement accommodated in the shaft and operated by means of hydraulic fluid, wherein the arrangement consists of a hydraulically actuatable piston arrangement. A connecting pin, which connects the sliding sleeve to the hydraulic piston arrangement, is provided, which extends through a hole with axial play that is arranged transversely in the shaft. The familiar gear shifting device disadvantageously requires a very complex layout since the actuating device or piston arrangement is accommodated in the shaft. This affects the manufacturing costs of the familiar gear shifting devices negatively. 
   It is the object of the present invention to suggest a transmission shift system of the aforementioned kind, which comprises a synchronizing device with a simple design and which additionally can be selected as easily as possible. 
   SUMMARY OF THE INVENTION 
   A transmission shift system, according to the invention, is suggested in which the piston, which is provided as the sliding sleeve, is actuated hydraulically, wherein a self-locking synchronizing device is provided. The piston is axially arranged, displaceable on a shaft by means of hydraulic actuation and is connected with the shaft in a non-rotatable fashion. Furthermore, the piston is provided on the circumference of the shaft, resulting in a synchronizing device with axial friction surfaces on the idler wheel with a very simple design. Beneficially, only a certain hydraulic pressure level is required for actuation. The pressure level can, therefore, be selected via simple switching valves. 
   Within the framework of a further beneficial development of the invention, it can be provided that the synchronizing device comprises at least one piston that can mesh with a selected idler wheel. The piston is, therefore, displaced axially on the shaft by means of hydraulic actuation. To return the piston to an idle position of the synchronizing device, at least one suitable return spring element or the like can be provided. 
   The piston can preferably be designed as an annular flange that is step-shaped in its cross-section, wherein it is seated in a piston carrier, which is firmly connected to the shaft. Between the piston and the piston carrier, a piston chamber is provided for hydraulic actuation, which is preferably supplied with pressure oil. The piston, which is designed as an annular flange, can be equipped on its outer step with first interior gear teeth as the coupling teeth to the idler wheel and with second interior gear teeth on the inner step to connect to the shaft. 
   Pursuant to a further development of the present invention, the idler wheel which is seated rotatably on the shaft and can comprise running gears, which are positively connected to additional torque-transmitting elements. Furthermore, coupling teeth can be provided for positive connection with the piston on the idler wheel in the shifted-through state. 
   The idler wheel can preferably be seated on a profile element or the like of the shaft. It is also conceivable for a rolling or plain bearing to be used to seat the idler wheel. 
   The piston carrier can alternatively also form a single component with the shaft. To seal the piston chamber at least one sealing element can be provided, which is preferably installed in a corresponding recess on the piston carrier. It is also possible to arrange one or more sealing elements, such as sealing rings or the like, on the piston. 
   A further development of the present invention can provide that in the axial direction between the piston and the idler wheel a first friction plate with inside and outside teeth is arranged. The outside teeth are preferably chamfered at least on the end facing the piston so that the first friction plate acts as a locking element during the synchronizing phase and represents a self-locking synchronizing device. Furthermore, a second friction plate can be arranged on the side of the idler wheel that faces away from the piston. It is especially beneficial if the first friction plate and the second friction plate are identical in design so that the production requirements are reduced. 
   Alternatively a third friction plate, which forms an outside plate, and a fourth friction plate, which forms an inside plate, can be arranged on the transmission shift system pursuant to the invention, wherein the inside plate can be arranged between the outside plate and the second friction plate. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example, with reference to the accompanying drawings in which: 
       FIG. 1  is a cut sectional partial view of the transmission shift system pursuant to the invention with synchronization in idle; 
       FIG. 2  is a diagrammatic view of the positions of the various gear wheels in relation to one another pursuant to  FIG. 1 ; 
       FIG. 3  is a cut sectional partial view of the transmission shift system pursuant to the invention with synchronization in the locking or synchronization position; 
       FIG. 4  is a diagrammatic view of the positions of the various gear wheels in relation to one another pursuant to  FIG. 2 ; 
       FIG. 5  is a cut sectional partial view of the transmission shift system pursuant to the invention with synchronization in the shifted state; 
       FIG. 6  is a diagrammatic view of the positions of the various gear wheels in relation to one another pursuant to  FIG. 5 ; 
       FIG. 7  is a cut sectional partial view of another embodiment of the transmission shift system pursuant to the invention with synchronization; and 
       FIG. 8  is a diagrammatic view of the positions of the various gear wheels in relation to one another pursuant to  FIG. 7 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In  FIG. 1 through 6 , a possible embodiment of the transmission shift system with a synchronizing device, according to the invention, is illustrated. 
   The synchronizing device comprises a piston  1 , which is designed as a step-shaped annular flange and comprises first interior teeth  12  as the coupling teeth with an idler wheel  3  on its outside step and second interior teeth  13  on its inside step for the purpose of connecting with a shaft  9 . The piston  1  is axially displaceable on the shaft and is connected to it non-rotatably, wherein the piston that is designed as an annular flange is provided on the circumference of the shaft. The end of the first interior teeth of the piston  12  or of the sliding sleeve facing the idler wheel  3  is chamfered at least in part. 
   In the axial direction, a first friction plate  2  with interior teeth  17  and exterior teeth  18  is arranged between the piston  1  and the idler wheel  3 , wherein the side facing the idler wheel  3  serves as a friction surface. During a synchronizing phase, the first friction plate  2  is also used as a locking element resulting in a self-locking synchronizing device. The exterior teeth  18  of the friction plate  2  are chamfered on the end facing the piston  1 . In the radial direction, the friction plate  2  can rotate in its interior teeth in relation to the shaft  9  around the intermediate space between two adjoining teeth of the first interior teeth  12  of the piston  1 . For this purpose, the interior teeth of the friction plate  2  are arranged with play to the shaft  9 , which is designed to be as large as the intermediate space between two adjoining teeth of the first interior teeth  12  of the piston  1 . 
   The idler wheel  3  comprises running gears  15  and coupling teeth  16  with chamfered teeth on the side facing the friction plate  2 . In a non-shifted state, i.e. in idle, the idler wheel  3  can rotate freely on the shaft  9 . The idler wheel  3  is seated rotatably on a profile  20  of the shaft  9 . 
   In the axial direction, a second friction plate  4  is provided behind the idler wheel  3 , the plate  4  comprising only one set of interior teeth  17 ′ toward the shaft  9 . On the sides of the friction plates  2 ,  4  that face away from the idler wheel  3 , safety rings  7 ,  8  are provided, which support the friction plates  2 ,  4  in an axial direction. The friction plates  2 ,  4  contain a suitable friction coating on the friction surfaces. 
   The piston  1  is seated in a piston carrier  5 , which is firmly connected to the shaft  9 . The piston carrier  5  comprises a pressure oil feed line  10  for hydraulically actuating the synchronizing device and suitable sealing elements  21 ,  21 ′ for sealing the piston chamber  1 . Furthermore, return springs  6  are evenly distributed across the circumference of the piston  1 . The return springs  6  enable the piston  1  to return to its position in a non-shifted state. 
     FIG. 1  shows the transmission shift system in idle, according to the invention. In idle, the piston  1  is held against a stop on the piston carrier  5  by the return springs  6 . The piston chamber between the piston  1  and the piston carrier  5  is without pressure in this state. The idler wheel  3  can rotate freely on the shaft  9 , wherein axial play exists, between the idler wheel  3  and the respective friction plates  2 ,  4 . With respect to the circumferential direction, the first friction plate  2  assumes any random position in its rotational play in relation to the shaft  9 . 
     FIG. 2  illustrates that in idle, the chamfered teeth of the first interior teeth  12  of the piston  1  do not come into contact with the chamfered teeth of the exterior teeth  18  of the friction plate  2 . 
     FIG. 3  shows a locking and synchronizing position of the transmission shift system. The piston chamber between the piston  1  and the piston carrier  5  is fed with pressure oil in this position. Moving the piston  1  eliminates the axial play between the idler wheel  3  and the respective friction plates  2 ,  4 , and the friction plates  2 ,  4  are pushed against the safety rings  7 ,  8 . Due to the friction torque acting in the circumferential direction between the idler wheel  3  and the friction plate  2 , said plate is rotated against the piston  1  to its maximum rotational play. The chamfered teeth of the piston  1  rest against the chamfered teeth of the first friction plate  2 , as illustrated in  FIG. 4 . In this locking and synchronizing position of the transmission shift system, shifting of the piston  1  is prevented. 
   The circumferential force present on the friction plate  2  due to the friction torque is greater than the circumferential force acting on the friction plate  2  from the chamfered tooth surfaces of the piston  1 . This means that the piston  1  remains locked as long as a speed differential, and hence a corresponding friction torque, exists between the shaft  9  and the idler wheel  3 . 
     FIG. 5  shows the shifted state in which the idler wheel  3  is connected positively to the shaft  9  via the piston  1 . As soon as the speed differential between the idler wheel  3  and the friction plate  2  moves toward zero, the circumferential force present on the first friction plate  2  that is from this friction torque disappears. The piston  1  is then able to rotate the friction plate  2  back so that the teeth of the first interior teeth  12  of the piston  1  can be guided through the intermediate spaces between the teeth of the exterior teeth  18  of the first friction plate  2 , as is indicated in  FIG. 6 . The piston  1  can hence be shifted so that the piston  1  with the idler wheel  3  is positively connected with the shaft  9 . 
   To release the connection it is only necessary to eliminate the applied pressure of the piston chamber between the piston  1  and the piston carrier  5 . The return springs  6  then slide the piston  1  back into its starting position. 
   Should greater friction torque be required on the synchronizing device, another embodiment of the transmission shift system as illustrated in  FIGS. 7 and 8  can be used. 
   The embodiment shown there represents a possible expansion of the previously illustrated embodiment. In this synchronizing device a third friction plate  11  is provided as an exterior plate and a fourth friction plate  19  is provided as an interior plate on the side of the idler wheel  3  that faces away from the piston  1 . The third friction plate  11  also contains interior teeth  17 ″ for the purpose of connection with the shaft  9 . 
   This way the number of friction surfaces can be increased to 4 in the embodiment illustrated here. The number of friction surfaces can be further increased beyond the number shown here. 
   
     
       
             
           
             
             
             
           
         
             
                 
             
             
               Reference numerals 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
                1 
               piston 
             
             
                 
                2 
               friction plate with interior and exterior teeth 
             
             
                 
                3 
               idler wheel 
             
             
                 
                4 
               friction plate with interior teeth 
             
             
                 
                5 
               piston carrier 
             
             
                 
                6 
               return springs 
             
             
                 
                7 
               safety ring 
             
             
                 
                8 
               safety ring 
             
             
                 
                9 
               shaft 
             
             
                 
               10 
               pressure oil supply line 
             
             
                 
               11 
               third friction plate 
             
             
                 
               12 
               first interior teeth of the piston 
             
             
                 
               13 
               second interior teeth of the piston 
             
             
                 
               15 
               running gears 
             
             
                 
               16 
               coupling teeth of the idler wheel 
             
             
                 
               17, 17′, 17″ 
               interior teeth on the friction plates 
             
             
                 
               18 
               exterior teeth of the first friction plate 
             
             
                 
               19 
               fourth friction plate 
             
             
                 
               20 
               profile 
             
             
                 
               21, 21′ 
               sealing rings/elements